First, VTEC system profile
    The Honda Accord is a luxury sedan with a sports car with a variable valve timing and a valve lift electronic control (VTEC) system. The engine has four valves per cylinder. When the engine is running at low speed, the main intake valve is opened normally with the opening degree, and the auxiliary intake valve is only slightly opened to prevent the fuel from accumulating in the air inlet. When the engine is running at high speed, the main intake rocker arm and auxiliary intake Rocker arm and the middle of the intake rocker connection, so that the valve opening increases. Between the three intake rocker arm, there is a synchronous piston to control the connection or separation of the three rocker movements.
    The hydraulic pressure acting on the timing piston causes the synchronized pistons A and B to move in the same direction, and when the hydraulic pressure is reduced, the stop piston and the return spring move the synchronizing piston backwards.
    The use of VTEC system can reduce the engine fuel consumption, improve power output. When the engine is running at low speed, the eddy current is generated in the combustion chamber due to the difference between the main intake valve and the auxiliary intake valve, thereby improving the combustion efficiency and reducing the engine fuel consumption. When the engine is running at high speed, the output power of the engine increases as the opening degree of the main and auxiliary valves increases.
    Low speed
    The main rocker and the secondary rocker arm are not connected to the middle rocker arm, but are driven by the two cams at A different time and height. The secondary cam B is very small, so the intake valve is only slightly open. Although the rocker arm is moving with the central cam on the camshaft, it does not have any effect on the valve opening in the low speed state.
    High speed state
    At high speed, the piston moves due to oil pressure, so the main, secondary, and three rocker arms are traversed by two synchronized pistons, and the three rockers move together as a component. In this case, all the rocker arm by the C cam drive, so that the valve open and closed, and change the valve timing to adapt to the engine high-speed conditions.
    3. Control system
    The control system of this body at any time to monitor the operation of the engine conditions, such as load, speed per minute, speed and so on. This information is sent to the Engine Control Center (ECM), which determines when the valve lift should be changed.
    The timing of the valve change is:
    Speed: 10km / h or faster;
    Engine cooling water temperature: 10 ° C or higher.