Fuel And Emissions System Description - VTEC System

Fuel and Emissions System Description - VTEC System

VTEC

The VTEC system changes intake and exhaust valve lift characteristics (in normal lift and pause modes) to improve fuel economy. Two rocker arm oil control solenoids in the engine oil passage that leads to the intake and exhaust rocker arms controls the intake and the exhaust valve lift. The engine oil pressure is monitored by two rocker arm oil pressure sensors.

Operating Conditions

Start running

The engine runs on normal valve lift mode 1.

High acceleration from low speed

The engine runs on normal valve lift mode 1.

Low speed cruise

The intake and exhaust valves pause to reduce valve spring compression and pumping loss.

High acceleration from high speed

The engine runs on the normal lift cam. During an uphill run or an abrupt acceleration, the engine runs on normal valve lift mode 2 for about 2 seconds to check the VTEC system, then it returns to normal valve lift mode 1.

High speed cruise

The engine runs on normal valve lift mode 1.

Deceleration

The intake and exhaust valves pause and reduce engine braking force.

Stop

The rocker arm changes to normal valve lift mode 1, and prepares for engine restart.






System Operation

Normal valve lift mode 1 (default)

Rocker arm oil control solenoids A and B are both off. Engine oil pressure from the oil pump passes the spool valve and the rocker arm. Engine oil pressure is applied to the intake side pistons and the exhaust side pistons. This causes the primary and secondary rocker arms to shift the valves to their normal lift positions.










Normal valve lift mode 2

Rocker arm oil control solenoid A is off and rocker arm oil control solenoid B is on. Engine oil pressure from the oil pump passes the spool valve and the rocker arm. Engine oil pressure is applied to the intake side pistons and the exhaust side pistons. This causes the primary and secondary rocker arms to shift the valves to their normal lift positions. By turning off rocker arm oil control solenoid A only, the spool valve is changed to normal valve lift mode 2 quickly. It enables the valve lift to change from valve pause mode to the normal lift position quickly. In this mode, the VTEC system is checked for about 2 seconds.










Valve pause mode

Rocker arm oil control solenoids A and B are both on. Engine oil pressure from the oil pump passes the spool valve and the rocker arm. Engine oil pressure is applied to the intake side pistons and the exhaust side pistons. This causes the primary and secondary rocker arms to separate, shift the valves to their pause positions.