Nowadays, new cars are required to have the least possible impact on the global environment.
Environmental laws enforce more rigorous regulations year after year, creating more needs for greener vehicle components.
Among them, the variable valve timing (VVT) actuators have attracted a lot of attention in recent years.
VVT is a process that alters the timing of valve lift events in a series according to the conditions of the vehicle, and is often used to improve performance, fuel economy or emissions.
Aisin started to develop VVT in 1986.
The first model with Aisin's geared VVT actuator was Toyota’s Corolla Levin that hit the market in 1991.
The gear-type VVT had a poor reputation.
It had unsolved disadvantages, and that ousted it from the competition with other vehicles.
It kept losing games. No one had a solutions. The situation got to the extent that rumors heard offstage—“The team will soon be dismissed unless they solve the problems.”
VVT（Variable Valve Timing）
VVT adjusts the opening/closing timing of the intake and exhaust valves using camshafts.
An oil control valve (OCV), responsible for controlling oil flow into the camshafts, determines the rate of rotation of the VVT. (Vane-type)
A VVT works in a system that uses mechanical gears or hydraulic vanes (See the figure below). The gear-type VVT was the mainstream until the mid-1990s.
It has some drawbacks—high machining accuracy was required and the mechanism tended to be complicated and bulky.
Gear-type VVTs inevitably produce considerable friction and are slow in response. To circumvent these negative factors, Aisin, in 1986, started developing a compact, light-weight vane-type VVT.
Back then, no vehicle had a vane-type VVT. The project, which had proceeded to the phase of prototyping, was hindered by technical difficulties, failed to produce anything as efficient as the gear-type VVT, and eventually, was put on hold.
Engine System Engineering at Aisin decided to shift to the gear-type like other component suppliers.
And, the VVT that employed gears was a losing effort that earned a poor reputation.
Early summer in 1995, Engine System Engineering was forced to choose between gear or vane.
“No choice. We have to drop what we developed. Let's go the other way.”
The vane-type VVT left on hold came back to center stage.
The new project targeted a straight 6-cylinder engine to be launched by Toyota.
In just about two months, the team members created a system meeting the performance and cost requirements.
Their work was entered in the competition with high expectations.
However, again, the team failed to please the goddess of victory.
The winner of the game was a competing company that presented a system similar one in terms of the performance and pricing.
“There’s no way that our technology will turn into a product......”
Disappointment spread among the project members.
How Vane-Type VVT Works
The vanes are angled by engine oil pressure to adjust the timing of the valve opening and closing.
The head of Engine System Engineering encouraged the team members to go ahead.
“Toyota may be a giant, but there are a lot of auto manufacturers out there around the globe.
Why don't we look outside the domestic market?
Europe is a big market. We're going to play games there.”
His words marked the restart of the project. In November 1995, the team flew to Europe and made visits to all the auto manufacturers there.
Aisin was not a brand known to them. It was hard to find a manufacturer willing to have talks with someone from the company.
Only Renault Sport, the motorsport, performance and special vehicles division of Renault, showed some interest in the VVT system of Aisin.
Early in 1996, the first cars from Renault Sport equipped with an Aisin-made VVT won a race.
That was a turnaround. Aisin slowly came to be known to European car manufacturers and started to receive orders from Renault.
The Vane-type VVT took its first step, but there was long a long way to go until its great success.
Between design duties, the project task force and Aisin Europe members kept visiting Europe-based car manufacturers.
Upon the third visit to BMW, Munich, they got an opportunity to present the vane-type VVT.
After a series of negotiations, the German multinational company requested Aisin to work with local parts suppliers to furnish technical details in a package, indicating that it recognized the superior cost-effectiveness and responsiveness of the vane type over the dominant gear type.
But, it was just a start.
BMW required “a VVT on the exhaust valves as well.”
Early and late exhaust valve closing can also reduce emissions. A system with a VVT also for exhaust valves would be more efficient and detailed in terms of the exhaust control. That was what the auto manufacturer wanted. Though, there was a lot to technically overcome. Back then, no vehicle with exhaust valve control existed on the market.
To make what has requested happen, the vane home position had to be set at the largest angle to allow the valves to close and open at the earliest in the exhaust VVT.
However, in a VVT, the hydraulic pressure is the factor that determines the position of the piston, thus when the valves open and close. With no hydraulic pressure applied, the vanes stop at the smallest angle at which the valves open and close at the latest.
The requirement, in short, was to position the vanes at the largest angle even when no hydraulic pressure is applied.
Largest and Smallest Angles
Usually, the car engine drives the vanes to keep them at the smallest angle position. BMW asked to position the vanes at the largest angle position even when no hydraulic pressure was applied.s