July 30, 2012
July 30 – Atsugi, Kanagawa – Takamasa Ueda, expert leader, and Takeshi Sato, manager, from Nissan’s Powertrain Engineering Division discuss the downsized, supercharged engine used in the new Note hatchback.
Q1. Why downsize?
We wanted to select a smaller engine to improve fuel efficiency and reduce carbon dioxide emissions. We have also applied a supercharging system to a three-cylinder engine to improve performance and to make the car more fun to drive.
Before we decided to apply the supercharging system, we considered using a turbocharger. In the end, we selected a supercharger which is suitable for smaller engines.
We actually have experience with supercharged and turbocharged versions of the Nissan March in the Japan, which we made over two decades ago. When we developed the new supercharging system for this engine, we took full advantage of the development knowhow we have fostered over the years.
Q2. What are the technical details specific to the the new engine?
It is a strength of Nissan that we have been continuously developing technologies to improve fuel efficiency by reducing friction and raising the compression ratio. We combined these advanced technologies when we developed this engine.
It is essential to reduce the friction losses generated when the engine is running. To do this, we’ve applied our unique bore-circularity machining technology to the cylinder block to reduce the friction there.
Secondly, we use a variable displacement oil pump which allows us to control the flow of oil for better overall engine lubrication. This reduces drive losses and contributes to improved fuel efficiency.
We also use a specific coating technology called hydrogen-free diamond-like carbon (DLC). Although DLC is a common technology, our hydrogen-free DLC coating can further reduce friction.
It’s very important to optimize the compression ratio to improve engine performance. A higher compression ratio can convert fuel energy into engine power more efficiently during combustion. In other words, increasing the compression ratio is one measure to improve engine efficiency and increase fuel economy.
However, there are limits to increasing the compression ratio because a higher compression ratio causes knocking in gasoline engines.
While a supercharger increases performance, it also means sending hot air into the combustion chamber, which adds to the challenge of preventing knocking. To prevent knocking, it is necessary to release heat caused by the hot compressed air in the combustion chamber .
Direct-injection technology, where fuel is injected into the combustion chamber, is one way to reduce heat, as fuel has a cooling effect when it vaporizes.
This technology enables an engine with a supercharger to function with a higher compression ratio. This is the main reason that we have applied direct injection technology to this engine.
To release heat from the combustion chamber, we have also applied special exhaust valves that are filled with sodium. Additionally, we optimized the design of the water passages in the cylinder head to cool the combustion chamber.
Q3. What are the advantages of a smaller engine?
There are other benefits of using a smaller engine. A compact engine is a big advantage for increasing cabin space. The lighter engine also allows the use of lighter parts which helps us to reduce the overall vehicle weight.
Put simply, this engine is relatively powerful despite its compact size.
We want drivers to enjoy the great fuel efficiency when driving on urban roads, and to enjoy the car’s driving performance on highways or mountain roads. There, they can experience the increased torque and acceleration brought about by the supercharger.