How VTEC Works
Honda’s VTEC (Variable Timing and Lift Electronic Control) system was groundbreaking because it was the first variable valve timing system widely available on a consumer car. In addition to being a pioneer in the field of electronic valve control, Honda has continued to maintain a position on the cutting edge of advanced engine management technology. Although there have been improvements to the VTEC system over the 2 decades since it has been introduced, the basic concepts behind all the incarnations of Honda’s VTEC system are the same. Here is a quick introduction to Honda's VTEC technology and a basic explanation of how it works.
What Variable Valve Timing Does
Although terms like variable valve timing may seem like high-tech vocabulary, the fact is that the VTEC system is actually just a clever solution to a very simple problem. The problem has to do with the limitations of the piston engine. While we are all used to the way that gasoline engines perform, the fact is that they are actually only able to produce peak power in a very narrow range of conditions. One of the main limitations that a gas engine must deal with has to do with the valve timing. The configurations for valve operation that yield good performance at low engine RPMs (Revolutions Per Minute) aren’t as efficient at higher RPMS and vice-versa. The solution that Honda came up with for this problem is actually to provide the engine with two different cam profiles and allow it to select the best one for each condition. One cam profile offers a smooth idle as well as good performance and torque at slower engine speeds. The other profile produces maximum power at higher engine speeds. Allowing the engine to have two different settings on command helps it to operate more capably and efficiently at a wider range of speeds.
How VTEC Works
The challenge with any variable valve timing technology is basic: How do you switch cam profiles on an engine while it is operating? The VTEC system accomplishes this in a very clever but simple way. The process is easier to understand if you know the components that comprise the VTEC system.
- Engine Computer
- RPM (Engine Speed) Sensor
- Hydraulic Solenoid (VTEC switch)
- Variable Position Rocker Arm
The VTEC switching process is performed as follows:
- The engine computer monitors the RPM sensor to determine the correct cam profile for the current engine conditions.
- If a switch must be made, the engine computer then activates or deactivates the VTEC solenoid. For this example, we will assume the engine computer is engaging the VTEC solenoid for high-speed operation.
- With the VTEC switch engaged, a passage is now opened connecting the oil pump directly to the variable position rocker arm. Pressurized oil flows in.
- The pressure of the oil in the passage engages a pin inside the rocker arm, locking an extra cam follower in place, which selects the new setting.