A High Power, Wide Torque Range, Efficient Engine with a Newly Developed Variablea-Valve-Lift and -Timing Mechanism 890675

A variable valving system was developed. This system has two cam profiles, one for low speed and one for high speed. A 1.2-litre DOHC experimental engine using this system was made and mounted in the body of a 2-1itre class passenger car. Test results of this car were compared to those of the same car with its original engine. The test car showed better results in every area of driving performance, in mode-fuel-econorny and in noise tests. This paper presents the mechanism, operation and test results of this variable valving system, the 1.2-litre experimental engine and this passenger car.

THE PERFORMANCE AND EFFICIENCY of the passenger car gasoline engine have been greatly improved: primarily as a response to exhaust-gas emission regulations and the oil crises. These improvements have been achieved mainly through the development of control technologies to optimize many parameters such as ignition timing and air fuel ratio precisely according to driving conditions.

It is well known that many efforts have long been made to improve engine performance and efficiency by developing engine mechanisms themselves to be variable and controlled according to driving conditions. In particular, extensive studies have been made to develop variable valve timing and valve lift mechanisms.

It is also well known that the variable valving system can be applied to improve low speed engine performance. Beneficial effects can also be obtained in fuel economy during idling and for partial loads and in low speed torque. If applied to improve high speed engine performance, the specific output can also possibly be increased. (1)*

What mechanism will be necessary to make variable valving more effective for both low and high speed engine performance? First, the mechanism should be able to give optimum cam profiles required for both low and high speed, and such cam profiles should be set independently without restricting each other. Second, when a higher specific power is required, a higher speed than that required by conventional engines will be required. Thus, the variable valving mechanism should have the potential for higher speed. These were the targets.

Because of the beneficial potential of such a mechanism, it was adapted to a 1.2 litre DOHC experimental engine with four valves per cylinder. This engine had flat torque characteristics over a very wide range of speeds, a very high specific power and low-speed torque characteristics suitable for passenger cars. It was then mounted in the body of a 2 litre class passenger car for the purpose of conducting driving tests. The purpose of this series of tests was not only to evaluate the potential of this variable valving system but also to examine the possibility that such an engine having the characteristics described above can greatly reduce the displacement of passenger car engines without any negative effects compared to large-­displacement engine.