Variable Valve Timing And Lift Electronic Control System (Vtec) - Honda Acura NSX 1991 Service Manual

Variable Valve Timing and Lift Electronic
Control System (VTEC)
Lost Motion Mechanism
The mid rocker arm is always driven by the high-speed cam lobe, even at low speeds. At low speeds, the lost motion
mechanism keeps the mid rocker arm in contact with the high-speed cam lobe. At high speeds, the lost motion
mechanism acts as part of the valve spring load.
CAM PROFILE
LOST MOTlCiN ASSEMBLY
Hydraulic Pressure Control
Spool valve/hydraulic pressure
The solenoid valve, in response to a signal from the PGM-FI ECU, closes the oil passage to the rocker arm at low speed.
This cuts oil pressure to the hydraulic pistons in the rocker arms so the arms operate independently. At high speed, the
ECU opens the solenoid valve. The increased oil pressure causes the hydraulic pistons to lock the primary, secondary,
and mid rocker arms together.
The oil pressure switch serves as a sensor to determine if the switch-over has taken place in response to the ECU signal.
5-8
GUIDE HOLDER GUIDE HOLDER
Mechanism
switch
I I
OIL PRESSURE
SPOOL VALVE