[TMS] Suzuki Develops Throttleless Miller Cycle w/ 3D Cam

Oct 30, 2007
Motohiko Hamada, Nikkei Automotive Technology
The "full-throttle" state. The cam is at the right end. The left end of the cam, the area with high cam threads, pushes the roller.
The "full-throttle" state. The cam is at the right end. The left end of the cam, the area with high cam threads, pushes the roller.
[Click to enlarge image]
The "fully-closed throttle" state. When the cam is pushed to the left end by turning the central feed screw, the left end of the cam, the base circle, faces the roller.
The "fully-closed throttle" state. When the cam is pushed to the left end by turning the central feed screw, the left end of the cam, the base circle, faces the roller.
[Click to enlarge image]
Prototype engine. The motor is mounted on the head (at the right side of photo).
Prototype engine. The motor is mounted on the head (at the right side of photo).
[Click to enlarge image]

Suzuki Motors Corporation developed a valve operating system driven by a three-dimensional cam. It exhibits the prototype engine at the 40th Tokyo Motor Show.

It can default the throttle valve and operate by Miller Cycle. The fuel consumption and the torque are improved by 20% and 6%, respectively. The company intends to commercialize it in a few years.

The cam is shaped three-dimensional. The left end of the intake side is enlarged to allow bigger lift ranges. The lift on the exhaust side stays almost the same, but the cam threads are winding-shaped for variable timing (bottom side).

The cam, which is independent from the cam axis, can move freely in the axial direction. The key formed on the axis transmits the forces in the rotational direction.

For axial movement of the cam, an operational axis is placed between the intake cam and the exhaust cam in parallel to them. The operational axis is moved right and left by ball screws to control the contact area of the cam and the follower.

The arms extended toward the both sides from the operational axis move the cam in the axial direction. A bearing placed between the arms and the cam prevents the transmission of rotational forces.

The stroke of the operational axis is about 30mm. When the cam is positioned at the right end, its left edge, the area with high threads, pushes the roller. This is when it reaches the "full-throttle." The cam in the back is for intake, and the one on the front side is for exhaust, which is not shaped as sharp as the one in the back.

When the cam reaches the left end, the left end of the cam, the base circle, faces the roller. The lift amount reaches zero at this point. This is when it reaches "fully-closed throttle."

One cam follower drives two valves, which forms one cylinder. The roller is 27mm and the cam base is 36mm in diameter. It is a "point-contact" type but has a long lifetime because its rolling friction is equivalent to that of a ball bearing.

The cam is manufactured by plastic forming, followed by grinding and the final process of shot pining.

The three-dimensional shape is formed by a grinding stone that has a curved outer circumference. A general grinding machine priced about ¥20 million is used, but this process requires 4 minutes and the NC data is 200 times of the generally used cams. The company will find a way to skip the grinding process in the future.

The prototype is a 638cc inline 4-cylinder engine. It may be applicable to vehicles other than motorcycles because it is 319cc per one cylinder. Then, it will be competing with "Valvetronic" of BMW, "WEL" of Nissan and "Valvematic" of Toyota.

Compared with those engines, the number of increased parts is less and the friction loss is smaller in this system. The head is higher by only about 40mm.

But the motor area of the prototype engine is largely swollen up. It is a design suitable for motorcycle engines, in which the width matters rather than the height. It could be lowered if the motor layout is changed.