VTEC

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VTEC ( V ariable Valve T IMing and Lift E lectronic C ontrol) is an introduced in 1983 for motorcycles technology from Honda for variable valve control in engines .

Purpose of the system

A variable valve lift adjustment is required in order to achieve both an overall higher torque level at low speeds and a higher maximum output at high speeds in high-revving sports engines . This is intended on the one hand to prevent weak starting and thus increase suitability for everyday use, and on the other hand to enable a sportier engine setup from a predefined engine speed. For this reason, the engine has two camshaft profiles , as the valves are not actuated directly, but via rocker arms controlled by oil pressure . VTEC was conceived by Honda's engine designer Kenichi Nagahiro.

Depending on the engine design ( Eco -Motorkonzept or racing engine) is thus at a certain speed by oil pressure with a locking pin in the oscillating either another correspondingly differently shaped rocker arm rocker arm being added and the valve opening amount is increased and the opening time, or another exhaust valve per cylinder , which the performance at higher speed is beneficial. If the engine speed falls below this value, the exhaust valve or the additional rocker arm is switched off again by means of the retracting locking bolt and remains unused.

variants

DOHC-VTEC

The VTEC system is one way of equipping an engine with different camshaft profiles:

  • a profile optimized for consumption and smoothness for low revs and
  • a performance-optimized profile for high speeds.

Switching between the profiles is influenced by the following factors:

  • Load condition
  • Engine temperature
  • Water temperature
  • Engine speed
  • Vehicle speed

When the engine speed increases and all other factors give the green light for a switchover, a solenoid valve opens and fills an oil channel, the oil pressure of which actuates a locking pin that connects three separate rocker arms or roller rocker arms. The largest (dominant) cam now takes over the valve control for high speeds. The valve is now opened earlier and longer. In addition, the valve lift is increased by the "high" cam profile. The DOHC-VTEC system has these different profiles both on the camshaft responsible for the intake valves and on that for the exhaust valves.

DOHC-VTEC was first introduced in the passenger car sector in the 1989 Honda Integra, which was only sold in Japan . This had a 119 kW variant (160 hp) of the B16A engine. The American market first saw the VTEC system in 1990 in the Acura NSX . This used it in his V6 DOHC engine. From now on, DOHC-VTEC engines appeared in other Honda models as well. The first German models with the DOHC-VTEC system were the Civic , the CRX and the NSX in 1990/91 .

SOHC-VTEC

After the DOHC-VTEC system was very well received, VTEC was also installed in SOHC engines. The disadvantage of this transfer is that in SOHC engines, one camshaft is responsible for the intake and exhaust valves. The VTEC system can only be applied to the intake valves, as the space required by the spark plugs prevents variable control of the exhaust valves. In SOHC engines, the spark plugs must point into the combustion chamber at a certain angle in order to effectively ignite the mixture in the cylinder. This installation method prevents the exhaust valves from being given a VTEC cam profile.

SOHC VTEC-E

The E stands for economy . VTEC-E uses a modified type of VTEC. VTEC-E did not optimize the performance at high speeds, but increased the effectiveness at low speeds.

The camshaft in an engine with VTEC-E has two cam profiles for the intake valves. One of these profiles allows the first (and later the second) inlet valve to fully open. The other profile is used to open the second inlet valve minimally in the beginning. The valves are opened with roller rocker arms .

At low speeds, the first inlet valve is fully opened, while the second is minimally opened. This results in a better fuel-air mixture, which enables a very lean mixture. If the engine speed is increased, the second intake valve, which has only been opened minimally up to that point, is coupled to the fully opening first intake valve in order to ensure a sufficient mixture. This coupling of the valves is influenced by the control unit. It calculates the switchover point based on engine speed and load, vehicle speed and coolant temperature. When the engine is running at full load, the valve is switched on at 2700 min −1 , with partial load only at 3300 min −1 .

  • As with SOHC and DOHC VTEC, a small locking pin is used to connect both valves.
  • Cars with a VTEC-E motor have a green identification lamp with the inscription "ECONO" in the instrument cluster . When the engine is operating in an economical mode, the lamp is switched on.
  • In 1994, the Civic VEi with a VTEC-E motor was considered to be one of the most economical petrol engines in the world.

DOHC i-VTEC

Cylinder head with iVTEC technology

The i stands for intelligent VTEC system. The engine changes the valve opening times when starting and accelerating in order to provide optimal, high-torque performance. When driving smoothly and with no load, the inlet valves close later in order to keep fuel consumption as low as possible. The i-VTEC system expands the DOHC-VTEC by a phase adjustment on the inlet side. The phase can be adjusted here by up to 50 °, which on the one hand leads to lower consumption and on the other hand to more torque and thus more power.

Compared to the DOHC-VTEC (or SOHC-VTEC), programming is much more complex. Where 4 maps are required for the DOHC-VTEC (2 each for the ignition and the injection quantities), this is the case with the i-VTEC (4x6 + 2 maps, 2 each for ignition and injection quantity, and also for different phase positions (0-50 ° ) and the phasing as such for non-VTEC and VTEC)

3-stage VTEC

Honda also introduced a 3-stage VTEC system in select markets. It combines the working methods of the SOHC-VTEC and the VTEC-E. At low speeds only one inlet valve is opened (from the VTEC-E), at medium speeds both. At high speeds, the cam profile for high speeds is switched over (by the VTEC). This ensures low fuel consumption at low speeds, but also a high level of power output in high speed ranges.

The 3-stage VTEC was installed in the D15B engine of the EK3 (sixth Civic generation), which was not offered in Germany. The motor reaches at 7000 min -1 an output of 130 PS.

Vehicles with a VTEC engine

Civic Type R with i-VTEC engine

Automobiles

motorcycles

Comparable systems

The technology of variable valve control was also taken up and implemented by other manufacturers.

So have for example

and other manufacturers (Ford, Nissan, Porsche) developed comparable systems.

→ Main article: camshaft adjustment

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