What does iVTEC Mean?
Discussion
Hi guys
Whilst reading about the ATom I cam across a phrase "about 4900rpm you could feel the iVTEC kicking in".
I'd never previously investigated the actual meaning of iVTEC so searched the net for some explanation and at the following link found a very clear explanation that I thought was worthwhile posting here.
Check this out
http://www.hotrod.com/techarticles/engine/113_0307_vtec/
JC
Whilst reading about the ATom I cam across a phrase "about 4900rpm you could feel the iVTEC kicking in".
I'd never previously investigated the actual meaning of iVTEC so searched the net for some explanation and at the following link found a very clear explanation that I thought was worthwhile posting here.
Check this out
http://www.hotrod.com/techarticles/engine/113_0307_vtec/
JC
VTEC refers to a system Honda use to achieve different valve timing at high and low revs. Broadly there are two types of systems:
- multiple cam systems
This is what the Honda and Toyota system use. There are two cam lobes on each camshaft, which can operate each valve via a rocker system. The engine can switch between the two lobes using a hydraulicly operated pin, controlled electronically on recent systems, mechanically on earlier ones. One of the two cam lobes is suitable for operating at lower (i.e. before the "VTEC" point, ~5,000rpm) engine speeds: the other is a more racy cam (with longer valve opening and overlap) which would not allow a smooth idle and low speed operation, but it great at high speeds. Difficult to develop much further, since space limits the number of cams, followers and rockers you can have operating a single valve
- cam phasing systems
As used by Rover (VVT) and BMW (VANOS). These adjust the amount of advance and retard on the inlet and exhaust cams, and the extent of lift of the valve. Imagine a conventional cam opens the valves at 0 degrees. These systems can move the cam so that it can open the valves at say +8 degrees or -5 degrees. So although the cam profile is the same, the amount of overlap can be altered and the valve timing can be adjusted (you need different timing at high and low speeds, and at different torque loadings). I hope the lift point is self-explanatory?
Neither is perfect, and I don't see why in theory you could not combine the two. There are a raft of other variants as well. F1 cars now all use pneumatic valves where all the parameters can be altered at any rpm, which is the ideal world. However, you need pneumatic pressure before you can start the engine, which is not ideal in a road car that might be left at the airport for 3 weeks, or in a garage over winter. A lot of work is being done on electronic valve operation, but I've not heard of even operating prototypes being used in cars yet.
- multiple cam systems
This is what the Honda and Toyota system use. There are two cam lobes on each camshaft, which can operate each valve via a rocker system. The engine can switch between the two lobes using a hydraulicly operated pin, controlled electronically on recent systems, mechanically on earlier ones. One of the two cam lobes is suitable for operating at lower (i.e. before the "VTEC" point, ~5,000rpm) engine speeds: the other is a more racy cam (with longer valve opening and overlap) which would not allow a smooth idle and low speed operation, but it great at high speeds. Difficult to develop much further, since space limits the number of cams, followers and rockers you can have operating a single valve
- cam phasing systems
As used by Rover (VVT) and BMW (VANOS). These adjust the amount of advance and retard on the inlet and exhaust cams, and the extent of lift of the valve. Imagine a conventional cam opens the valves at 0 degrees. These systems can move the cam so that it can open the valves at say +8 degrees or -5 degrees. So although the cam profile is the same, the amount of overlap can be altered and the valve timing can be adjusted (you need different timing at high and low speeds, and at different torque loadings). I hope the lift point is self-explanatory?
Neither is perfect, and I don't see why in theory you could not combine the two. There are a raft of other variants as well. F1 cars now all use pneumatic valves where all the parameters can be altered at any rpm, which is the ideal world. However, you need pneumatic pressure before you can start the engine, which is not ideal in a road car that might be left at the airport for 3 weeks, or in a garage over winter. A lot of work is being done on electronic valve operation, but I've not heard of even operating prototypes being used in cars yet.
coxm said:
A lot of work is being done on electronic valve operation, but I've not heard of even operating prototypes being used in cars yet.
I thought the Renault F1 a few years ago (the one which had a very wide V angle, 2002 possibly) used electronic valves, they have gone back to a hydraulic set up now as it was not so reliable. On the other hand this site suggests I am wrong
http://scarbsf1.com/valves.html
Ben
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