HONDA The Power of Dreams

Ikuo Kajitani, who was employed in the First Design Dept at Honda's Tochigi R&D Center, was involved in the development of these four-valve engines. Through his experience in engine design, Kajitani had become convinced that Honda's next engine should offer a mechanism that could alter the timing of the valves.

"Characteristically," Kajitani said, "four-valve engines are known as high-revving, high-output machines. And for that reason we knew it would be quite difficult to achieve low-end performance if the engine's displacement were too small."

Problems certainly arose during the process of development. A reduction in the valve's interior angle, attempted in order to increase low-end torque, resulted in a broken timing belt and valve spring as the unit reached the upper range of revolutions. To address the problem, the development staff put in uncounted hours studying how to balance these two critical areas of engine performance. They knew they had already succeeded with their DOHC and SOHC powerplants, but to develop a new unit that would outperform its predecessors they would have to bridge the gap between the low end and the upper limit.

One group already had examined the idea of switchable valve timing. In January 1983, a year before the NCE program began, a research team was formed to study the mechanism as a means of enhancing fuel economy. Even though by the end of 1982 Honda engines were already capable of a world-beating 50 miles per gallon (mpg), there would be an effort to improve.

A possibility was thus identified through the study of a new valve mechanism. Specifically, it was believed that the installation of a new set of cam followers and rocker arms for high-speed operation on the intake and exhaust sides would help, along with the switching of cam hills according to engine speed. This was to be their solution to higher engine efficiency.

This was the so-called "valve stopping + variable valve timing" mechanism employed in the NCE program. As a core technology for Honda's proposed new line of engines, the mechanism then underwent a program of study and refinement under the careful supervision of Honda's research staff. Eventually the mechanism evolved into Honda's VTEC (Variable Valve Timing & Lift Electronic Control System) engine. Launched via the 1989 Integra, this innovative technology surprised the world with a new level of performance from a compact, fuel-efficient engine.

It all began in the planning stage, wherein the team identified approximately thirty new mechanisms and technologies they would need to introduce in order to secure a stable VTEC system. These included a valve-operating system with a hydraulic timing selector pin, a small hydraulic tappet mechanism built into the rocker arm, and weight-reduction techniques to achieve higher revolutions and output. However, time and resources were limited, and it would be nearly impossible to achieve all of their objectives. As a matter of efficiency, priority items were selected with an emphasis on satisfying the engine's product requirements. For the items selected, detailed specifications were set and technological feasibilities examined.

During the selection process, the team came across technologies they believed were unnecessary in meeting the target requirements, along with unverifiable technologies which, if found to be flawed, could affect the VTEC mechanism itself. For advice the development team arranged a consultation meeting with members of the evaluation committee, whereupon the development team listed items they had originally wanted to adopt but now wished to cancel.

The discussions produced no results, since both sides refused to give up any ground. Kajitani was not certain which technologies should be used and which should be set aside. He kept asking himself, "Is this technology genuine?" That was exactly what Kawamoto would say.

"When I wasn't sure whether to introduce a new technology, Mr. Kawamoto would ask me if the technology was genuine. If I could honestly answer 'Yes,' he'd say, 'Okay, then do it.' When he asked me if it was 'genuine' or not, I was confused about what to say. After all, sometimes it's difficult to tell what's genuine and what isn't. Personally, I thought of a technology as genuine if it had been in the market around for ten years, but Mr. Kawamoto had a different definition. Even so, a technology that's been for around ten years is one that's accepted by society. In that sense, there shouldn't be any problem adopting such a technology to all models."

Several consultation meetings were held, some of them deep into the night, and at last the committee members accepted the development team's request. Such difficulties were commensurate with the scope of their proposed achievement. The difficulties the team endured through its discussions with the committee helped bring the VTEC engine to life.

The start of development meant, of course, that the team would begin facing the first of many anticipated challenges. There was often fear in Kajitani's mind, as well. "I thought we might not be able to achieve it because the goal was too high," he said, recalling the many travails of project development.

It was quite difficult, for example, to balance the valve-timing lift against the load placed on the timing belt, which would increase at high engine speeds due to the spring and other factors. Although it was a problem needing a solution in order to achieve the target output, such an answer would not be easy to find. To make matters worse, they found that the low-speed single-valve timing system was not applicable because it had been patented by another company. After examining numerous countermeasures through laborious trial and error, the team decided to change the entire specification surrounding the valve operating system. Subsequently, they introduced the combination valve-timing system after reviewing the valve diameter, lift and port shape, and identifying settings to ensure sufficient output. Further, they created a lightweight driven pulley using high-density, high-strength sintered alloy, and modified its shape for reduced thickness. This resulted in a 10 percent lower moment of inertia. Through these efforts the team satisfied the requirement for timing-belt load while achieving its output objective.

Output across the full rev range was increased by widening the diameter of the intake valve from the conventional DOHC engine from 30 mm to 33 mm. Also, the team adopted valve timing and lift settings that were comparable to Honda racing engines in order to enhance volumetric efficiency. The improved output resulting from that technique actually served to improve performance at high speeds. Additionally, measures were taken to reduce intake resistance. At last, the goal was reached, with a full 160 horsepower at 7,600 rpm and a redline of 8,000.

Low-speed torque, an initial project objective, was obtained by changing the low-speed cam's setting from the traditional 35 degrees to 20/30 degrees ABDC (after bottom dead-center). This permitted the intake valve to close early, drastically improving the engine's volumetric efficiency. Since the engine now had higher efficiency at low speeds of operation, a broader torque band could be realized.

The implementation of new materials was certainly a factor in the successful application of these technologies. For example, since the VTEC engine's three cam followers must be positioned in a single bore, the camshaft offers relatively limited cam width. Therefore, the shaft must be designed to withstand high surface pressures. To achieve this, the team developed a new camshaft of cast steel. The shaft was made of new high-carbon, high-chrome cast steel alloy, which was given a combination of heat and surface treatments. As a result the unit's extreme rigidity increased its critical surface pressure by as much as 40 percent.

The VTEC engine had finally revealed its complete performance profile. However, the success of D-development only meant the start of a critical phase. In order to ensure absolute reliability in mass production and introduce the engine to the market with confidence, the team had to guarantee the functions of all mechanisms and parts. In addition to a significant responsibility for product reliability, the team had special expectations regarding the VTEC engine. Said Kajitani, "We all shared the determination to apply these technologies to every Honda model."