Global Engine for Next-Generation 125cc Scooters

About the Global Engine for Next-Generation 125cc Scooters

  • Introduction
  • Technical details

Technical details

Compact combustion chamber and air intake port

The combustion chamber has been made more compact through a design that takes into account burning velocity and cooling performance so that the engine can have plentiful torque, especially in the ranges the 125cc scooter actually uses.
Furthermore, the air intake port that connects to the combustion chamber has been newly designed with a smooth shape that does not impede the flow of the fuel-air mixture, resulting in a more responsive throttle in the low- to mid-speed ranges due to the higher flow velocity in the air intake port, even in the operating range with a low throttle opening angle.
Burning velocity increases through the flow of fuel-air mixture generated by a squish area opposite the spark plug. In addition, knocking resistance is improved by a water jacket that efficiently cools the combustion chamber and a highly efficient radiator. These factors allow an optimal ignition timing closer to MBT* to be set, contributing substantially to improved output and fuel efficiency.

Cross-sectional view of engine

Minimum advance for the Best Torque
Combustion Chamber
Comparison of fuel-air mixture flow

Offset cylinder and spiny sleeve

One technology for better fuel efficiency is the offset cylinder, which can efficiently transmit explosive power to the crankshaft by reducing the friction caused by the rubbing between the piston and cylinder.
To reduce blow-by gas and oil consumption, we added tiny spines to the outer surface of the cylinder's cast-iron sleeve. This spiny sleeve improves cooling performance and reduces the distortion of the cylinder bore during operation. Its first use in a small-bore engine was in the PCX. Furthermore, centrifugal casting makes the sleeve thinner and more even, resulting in a weight reduction for this engine.
In addition, making the inner diameter of the bore in operation closer to a perfect circle (roundness increased by 70% and cylindricity by 40%) lowers the tension of the piston ring. Combined with the offset cylinder design, this structure reduces friction loss even further.

Conceptual diagram of offset cylinder

spiny sleeve
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