With the imposition in Japan of a new tax on cars based on engine displacement, in the early 1980s many many car manufacturers decided to invest time and resources to develop their small engines, in order to guarantee the same time good performance and low fuel consumption.
One of the most interesting and famous solutions, still used today on many cars, is the very famous VTEC (Variable Valve Timing & Lift Electronic Control Unit) by Honda, a system for varying the opening of the valves which, by improving the volumetric efficiency at different rpm, has made it possible to increase performance and at the same time decrease consumption in the lower ranges of use.
30 years of fame
Invented by Honda engineer Ikuo Kajitani, this dual camshaft system was first introduced in 1989 in Japan aboard the Integra XSi and in Europe on cars such as the Honda Civic and Honda CRX.
But the greatest success came with the launch in 1991 in the USA of the Acura NSX, equipped with a 270 bhp 3-liter V6 VTEC, and in 1998 with the Honda S2000, the sports spider powered by a 2-liter VTEC with double shaft 240 HP cams, for an incredible specific power of 120 HP / liter.
The importance of the cam profile
As we all know, the cycle of an engine is divided into 4 main phases: intake, compression, ignition and exhaust. Engineer Ikuo Kajitani has decided to focus his attention on the intake and exhaust valves which are moved according to the shape of the cams. A different choice respects most of the other manufacturers who have instead decided to focus on supercharging.
The cams determine when and by how long a valve opens and how long it stays open. Simplifying the concept, it can be stated that the larger the cams, the greater the opening of the valves and the quantity of air sucked into the combustion chamber, the quantity of fuel injected and consequently the available power increase. .
Conversely, the use of smaller profile cams results in less valve opening. This implies less air drawn in, less fuel injected, less power available but also reduced fuel consumption.
A system with different cams
To overcome these two huge differences in the size of the cams, the Japanese engineer decided to replace the single cam lobe and the classic rocker with a multi-part rocker and two different cam profiles. The smaller profile is used at low revs to reduce fuel consumption.
When more load is required from the engine and when parameters such as engine oil pressure, engine temperature, vehicle speed, engine speed and throttle position reach certain conditions, a dedicated control unit operates a solenoid that with oil pressure it inserts a locking pin between the high rpm and low rpm rocker arms, activating the cams with more thrust profiling.
From this moment the valves can open more and for a longer time, thus increasing the engine power at high revs. This demonstrates how VTEC technology is able to combine fuel efficiency at low revs and performance at high revs.
Some subsequent solutions
With the success and advantages obtained from the introduction of VTEC, Honda decided in the following years to continue developing this technology trying to find new and even more efficient solutions. These include the VTEC variant with direct injection with double overhead camshaft, the VTEC-E, the 3-stage VTEC, the I-VTEC, the I-VTEC I and the Advanced VTEC.
The VTEC-E version, for example, aimed at reducing fuel consumption at low revs. In this range, in fact, one of the cylinder’s intake valves did not open completely, thus reducing the quantity of air and petrol inside the combustion chamber.
|Production period||from 1989 to today|
|Displacement||from 1.5 liters to 3.5 liters|
|Power||da 115 CV a 507 CV|
|Models||Honda S200, Honda Civic, Honda Integra XSi, Honda CRX, Honda Prelude, Honda NSX|
Source: Motor1.com Italia – News by it.motor1.com.
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