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									  Reducing fRicTion                                                                                                                      R
  Friction conflicts with the progress of the car and the engine must
  overcome it, requiring additional power... which is a handicap in terms
  of fuel consumption. All the moving parts of a car – engine, tyres, transmission –
  are sources of friction. It may not be possible to banish it completely, but
  reducing friction optimises the overall efficiency
  of the vehicle and helps minimise its polluting emissions.



                                                                                                                         Life on board



  bASic FActS                                                                                                      in SHort
  in mechanics, as soon as there       efficiency of a mechanical system.    The studies that Renault is
  is movement, there is friction,      In automobiles, this takes the        carrying out to reduce the friction   by rEducing Friction,
  so any wish to eliminate friction    form of reducing the power            of its vehicles have an impact        it iS poSSiblE to incrEASE
  completely would be utopian.         that an engine needs to deliver       on numerous aspects of fuel           tHE ovErAll EFFiciEncy
                                       under identical driving conditions,   consumption and, consequently,        oF tHE cAr And tHuS
  Reducing it, however, makes          and so cutting polluting              of exhaust emissions.                 to minimiSE itS
  it possible to improve the overall   emissions.
                                                                                                                   ExHAuSt EmiSSionS.
How doES it work?
there are two basic types               Electrical timing, which makes          Renault has created close links
of source of friction:                  it possible to dispense with the        with oil manufacturers, such as
those that are inherent in the design   camshaft and timing belt, will          Total, and tyre manufacturers,
of the vehicle and the technologies     further reduce internal friction        like Michelin. On these two points,
that it employs, and those relating     in the engine.                          the attitude of users is also of great
to external factors. With regard        • The gearbox is also the subject       importance. Used oil loses part
to the design of the vehicle,           of studies intended to minimise         of its lubricating qualities
numerous solutions have already         internal friction. In addition,         and becomes less effective
been found or are under study.          such new solutions as robotised         in opposing friction in the
• The engine contains numerous          gearboxes (see sheet) mean that         powertrain components.
moving parts. Friction is directly      the power used by the gearbox           • Tyres inflated to the wrong
linked to the contact between           to perform a gear shift is reduced      pressure, in addition to posing
surfaces. One of the effects            to the absolute minimum. External       a danger, can considerably
of making the pistons smaller           sources of friction are often linked    increase the rolling resistance
is a reduction in the size of contact   to the environment of the car           of the wheels. The tyres must
surfaces, and hence in friction.        or to consumables.                      effect the balance between
Downsizing (see sheet) is a move        • Aerodynamics (see sheet)              grip and rolling resistance.
in this direction.                      also plays a large part.                The right trade-off can only
• Valve timing is also a major          By improving the car’s penetration      be achieved for a precise
source of friction in the engine.       of the air, it reduces the car’s        contact surface between
To reduce it, Renault has equipped      resistance to forward movement          tyre and road, directly linked
some of its engines with a              at high speed, which can be             to tyre pressure.
roller bearing rocker arm. This         assimilated to friction with the air.   Oil and tyres are two aspects
configuration makes it possible         • Oil and tyres have a direct           that the driver must keep close
to reduce friction by up to 50%         impact on friction. To gain a better    watch of in order to maintain
depending on engine speed.              understanding of each problem,          the overall efficiency of his car.

                                                                                                                         December 2008

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