It took us million of years to evolve into human beings. The case with IC engines too is not very different, and the frugal yet powerful engines that power our cars today are a result of over several decades of work. The development curves of engines from different manufacturers may have been different, but they tried to modify certain key parameters to bring engines at this stage. VTVT / VVT etc. can be put under one such technology group. In this article, we discuss it in detail.
What are these technologies in essence and what do they do?
A normal engine (that does not use these technologies) breathes by opening / closing of intake and exhaust valves. The amount of lift that these valves have, the time at which they open and the duration of the lift during the combustion cycle are fixed in case of an engine that does not use the technology like VTVT, VVT etc. This is a compromise since the valve opening requirements for an engine while it is breathing at low RPM is not the same as when the engine is running at a higher RPM. These technologies effectively manage the valve timing and lift during the combustion cycle based on engine rpm.
What does the Acronyms VTVT / VVT / i-VTEC / VVT-i / Ti-VCT etc. mean?
VTVT – Variable Timing Valve Train
VVT – Variable Valve Timing
VVT-i – Variable Valve Timing with Intelligence
i-VTEC – Intelligent Variable Valve Timing and Lift with Electronic Control System
Ti-VCT - Twin Independent Variable Camshaft Timing
Are there any differences between these technologies?
All the technologies in the list except i-VTEC, vary only the valve timing in accordance with the engine RPMs. That is, advancing the opening of intake valves or providing valve overlap between intake and exhaust for optimum performance. The i-VTEC goes a step further and it can actually change the valve lift for greater flexibility.
How do these technologies affect the car’s performance?
Variable valve timing and lift make the engine more responsive to throttle inputs and all such engines generally have better low end power in comparison to the engines that do not use this technology. Another great benefit is the improved fuel efficiency and reduced emissions. (If you see the video above, you would notice how the valve lift changes with engine speed. The images present below show the variation that happens over different speeds.) The variation may look small, but in effect multiplied with engine speed has great impact over engine performance parameters.
Which manufacturers use these technologies?
Almost all manufacturers use these technologies in their advanced range of powerful engine. In fact it has become more or less a norm to use these, because without them, it would be impossible to meet the strict emission norms that are in place.
VTVT – Hyundai
VVT & VVTi – Toyota, Maruti Suzuki
i-VTEC – Honda
Ti-VCT - Ford
Are there any other lesser known derivatives of these technologies?
The VVT evolved into what is now known as VVT-i, similarly there are other technologies like VVTL-i which also creates variable lift, Dual VVT-i, Valvematic, Valvetronic, VVEL, VANOS etc. All these are technologies that aim to create variable valve timing or modify timing along with modifying the amount of lift.
More advanced valve trains instead of using stepped adjustment use the continuous variation. The Valvematic and Valvetronic are such systems that aim to create infinite adjustment of valves and timing and they used by Toyota and BMW respectively.
Is this the most advanced technology for valve trains?
No, Variable Valve Timing and lift comes with its own set of challenges and is not really cost effective. Although systems like Valvematic and Valvetronic provide infinite adjustment of valves, they cannot provide a flat opening curve for opening like a square cam would. Systems like Free Valve (Camless engine) that utilise pneumatic pressure to keep valves open / closed can do this and is considered a more advanced system.