1．Overview

Reducing CO₂ emissions and realizing a carbon-neutral society as soon as possible in response to the global warming problem is a common global issue. Although CO₂ reduction by electrification of automobiles is advancing, it is not uniform due to the effect of energy situation and degree of economic progress of each country. It is very important to reduce CO₂ emissions by improving the efficiency of internal combustion engines. On the other hand, the improvement of efficiency causes the complication of power train and becomes a factor of cost increase. The demand for automobiles is expected to increase mainly in emerging countries in the future, and CO₂ reduction must be accompanied by the improvement of efficiency as well as excellent economy. In order to solve these problems, the winner developed an engine with improved fuel economy while controlling cost by refining the design features of intake air, combustion, spraying and cooling which are the main elements of internal combustion engines.

Fig.1 New developed Engine (Left:NA Engine Right:HEV Engine)

2．Technical content

2．1　Engine specification

For the newly developed engine, the displacement and specifications are selected based on the key concept of 1.2 L3 cylinder long stroke. The main specifications are shown in Table 1 in order to achieve environmental performance, torque characteristics that overwhelm the class, and a compact size suitable for A-segment vehicles.

Table.1 Main specifications

2．2　Intake: High tumble straight port

The layout of the valve system of the cylinder head has been reviewed. The angle between the valve and the valve has been reduced. By combining it with a newly developed thin valve seat the height of the intake port has been lowered and the intake air flow has been introduced straight into the combustion chamber. A straight side flow shape which reduces the intake energy loss has been adopted and the tumble ratio has been improved by 30%.

Fig.2 Straight port shape

2．3　Combustion：Compact combustion chamber

The combustion chamber was made compact by valve pinching and squaring, and cooling loss was improved by S/V ratio reduction. Homogeneous combustion and high-speed combustion with 25% shorter combustion period compared with the conventional engine were realized by piston shape without valve recess and flat squish.

Fig.3 Flame propagation of combustion term

2．4　Spray : Dual port low-penetration spray

Fuel spray is required to achieve both reduction of unburnt loss and suppression of knocking by evaporative latent heat cooling. In the conventional fuel spray, the valve opening was aimed at and increase of unburnt loss was observed due to in-cylinder adhesion. In the newly developed low penetration spray, the installation layout aimed at the port throat was adopted and fuel was introduced by placing atomized spray on the intake air flow, which realized 14% reduction of wall surface adhesion.

Fig.4 low-penetration spray

2．5　Cooling : Parallel cooling system

Aiming at improvement of unburned loss and reduction of mechanical loss when the engine is cooled, a parallel cooling passage system was built into the cylinder block. By building a parallel cooling system into the cylinder block, miniaturization of the whole engine and reduction of circulating water quantity were realized. The continuous flow passage was made to be the shortest path and the structure was made to reduce unburned loss and mechanical loss by early engine warming.

Fig.5 Parallel cooling system

2．6　Constitution

Based on the concept of “simple, slim and compact”, the engine was shortened in the width dimension by using a small bore with a long stroke, and the engine was made lighter by reducing the weight of the moving system. The crank counter weight was made smaller in the height dimension and the body size was reduced to the size of 1.0L by reducing the size.

2．7　Efficiency and Cost

In the engine thermal efficiency map incorporating the above technologies, a significant improvement in efficiency has been realized compared with the conventional engine. The cost reduction of about 45% has been realized for the engine with the same thermal efficiency by polishing the design features and eliminating the complicated fuel consumption devices as much as possible.

Fig.6 Thermal efficiency

Fig.7 Cost index of engine

３．Summary

Using this technology, we have succeeded in developing a 1.0L engine for the A-segment that is equivalent in size to the conventional 1.2L engine and superior in efficiency and economy. This has contributed to customers by improving the product quality and contributed to CO₂ reduction market.

Soichiro Okudaira
Corporate member，DAIHATSU MOTORCO.,LTD.（1-1,DAIHATSUCHO,IKEDA CITY 563-8651）

Koichi Yorizane
DAIHATSU MOTORCO.,LTD.（1-1,DAIHATSUCHO,IKEDA CITY 563-8651）

Hidetomo Horikawa
DAIHATSU MOTORCO.,LTD.（1-1,DAIHATSUCHO,IKEDA CITY 563-8651）

Shinya Takedomi
DAIHATSU MOTORCO.,LTD.（1-1,DAIHATSUCHO,IKEDA CITY 563-8651）