26 September 2011
Honda Motor Co., Ltd. has developed new 700cc and 125cc engines for two-wheelers, as well as an accompanying lightweight, compact second-generation Dual Clutch Transmission, featuring a smooth, direct feel and excellent transmission efficiency.
700cc. This new engine is a liquid-cooled, 700cc, 4-stroke, in-line, 2-cylinder engine that fits into the mid-class range (displacement between 500 and 750cc) popular in Europe. Fuel economy exceeds 27 km/L (3.7 L/100km, 63.5 mpg US) WMTC (World Motorcycle Test Cycle) mode by Honda's calculation and achieves an approximate 40% improvement over other sports models in its class.
This new engine will be mounted on three models based on different concepts, which are slated for exhibition at EICMA2011 (69th International Motorcycle Exhibition) to be held in November in Milan, Italy.
Development of the new engine was performed to meet these requirements:
An engine that is easy to handle with plentiful torque in the range normally used, and which also delivers a pleasant, throbbing feel during sporty rides.
Top-class, fuel-efficient environmental performance best suited for the next-generation mid-class engine.
A lightweight, compact design that allows more freedom in the body layout and provides highly convenient space.
Honda determined the engine layout after examining a variety of engine types from numerous perspectives and decided on an in-line, 700cc, 2-cylinder engine with a 62° forward lean (cylinder assembly angle). To meet a wide variety of uses, two transmissions can be coupled with this engine: the second generation of Honda's innovative Dual Clutch Transmission, and a 6-speed manual transmission.
The new engine incorporates a wide variety of low friction technologies that aid better fuel economy. To improve fuel efficiency through better-controlled combustion while realizing a powerful ride in the low- to mid-rpm ranges, the bore-stroke ratio is set at 73×80mm. An optimized combustion chamber shape and optimum valve timing also contribute to achieve stable combustion. Resin coating is applied to the pistons, and lightweight aluminum material is employed for the first time in a motorcycle in the friction-reducing roller rocker arm.
Adoption of uneven-interval firing with a 270° phase crank and uniaxial primary balancer help realize an engine with a pleasant throbbing feel that also reduces vibration.
The layout of a branch intake port inside the cylinder head was chosen to have only one intake channel for two cylinders. This design creates deliberate interference between the two cylinders' intake processes to achieve precisely calculated changes to combustion timing.
In addition, to change the valve timing between the two in-line cylinders with one camshaft, the specifications provide for a cam with two timing routines for the intake valve. Through these measures, subtle combustion changes can be generated to give the engine a delightful, pulsating feel.
To maximize the efficiency of exhaust aftertreatment so that the three-way catalyst can be started promptly after the engine starts, the TWC has been placed directly beneath the exhaust ports. This design lets the combustion gas pass through the catalyst while the gas is still hot. In addition, a combination of measures, including the adoption of an electronically-controlled fuel injection system (PGM-FI), allows the engine to achieve an emission level approximately half the European emission standards (Euro 3).
Second-generation Dual Clutch Transmission. The Dual Clutch Transmission, developed for the first time by Honda for motorcycles and installed on the VFR1200F, is now lighter and more compact through a simplified hydraulic circuit and other design enhancements. A learning function has been added to each selected running mode to detect a variety of riding environments from city streets to mountain passes and automatically performs the most suitable shift control. Although it is an automatic transmission, the Dual Clutch Transmission delivers fuel economy on a par with manual transmissions as a result of its transmission efficiency.
125cc. The new 125c engine is developed for next-generation 125cc scooters and accommodates an advanced idle stop system for motorcycles. Fuel economy is approximately 25% better than that of conventional engines for scooters with the same displacement, according to Honda. This liquid-cooled, 125cc, 4-stroke, single-cylinder engine incorporates a wide range of low-friction technologies while packing its lighter weight in a more compact body.
This new engine will be mounted on a variety of 125cc scooters to be sold in many countries around the world and is planned for global rollout starting from 2012.
Development was performed to meet these requirements:
Powerful output and greater durability with an emphasis on practicality.
Excellent fuel efficiency suitable for the next-generation global-standard engine.
Contributing to CO2 reduction on a worldwide scale by applying to global models.
Realizing an affordable price.
Low-friction technologies such as an offset cylinder and a roller rocker arm are supplemented by such techniques as intelligent control to lessen friction during power generation and the first adoption of a shell-type needle bearing for the rocker arm shaft. Low-friction technologies applied include:
Offset cylinder reduces friction caused by the contact between the sliding piston and the cylinder.
Piston weight has been thoroughly reduced through CAE analysis.
A spiny sleeve with minute spines on the outer surface of the cylinder sleeve has been adopted to reduce oil consumption and improve cooling performance.
A shell-type needle bearing is used for the rocker arm shaft to reduce friction.
Smaller and lighter rollers together with an optimized cam profile and valve spring load.
Radiator core with high cooling efficiency has been adopted (approximately 1.5 times the efficiency of current models). This enables a smaller and lighter cooling fan on the back of the radiator and reduces friction loss by approximately 30%.
Transmission oil capacity is reduced 25% compared to current 125cc engines through modifications inside the transmission case in order to lower the oil agitation loss.
Bearings for each of the three axes in the transmission unit are exclusively designed according to the load received, resulting in an optimal set of specifications that lessen the rolling resistance inside the bearings. Friction loss has been cut by approximately 20% compared to the current engine (when running at 50km/h).
To increase combustion efficiency, Honda used a compact combustion chamber design incorporating burning velocity and cooling performance suitable for an engine that emphasizes torque characteristics in the rpm ranges actually used by a 125cc scooter.
Another step in this area includes redesigning the air intake port connection to the combustion chamber into a smoother shape that does not impede the flow of the fuel-air mixture. Optimal ignition timing is set due to improved knocking resistance created by a highly efficient radiator and a water jacket that efficiently cools the combustion chamber.
A smooth and quiet start has been realized through an electronically-controlled ACG starter, which serves as both a self-starter and a dynamo. An advanced idle stop system has also been applied.
A swing-back that returns the crank to its position before air intake is electronically controlled for easy restart, while a decompression mechanism mitigates cranking resistance arising from compression during engine start.
A wide-ratio continuously variable transmission with V-belt (V-Matic) utilizes a drive belt made of newly developed high-elasticity rubber. Both fuel efficiency and quietness are achieved through the efficient transmission of driving force by optimizing the lateral pressure applied to the belt, along with the durability of the belt.