Perspective illustration of automobile construction principle Volkswagen/Audi AVS variable valve lift

Volkswagen/Audi AVS variable valve lift mainly achieves optimal control of gas exchange for each cylinder through electronic valve lift switching on the exhaust camshaft and variable timing on the intake and exhaust valve camshafts. , the engine electronic control unit decides which cam to use based on the current engine load, and the smaller cam is only used at low speeds.

Variable valve lift has the following benefits: optimizes gas exchange; prevents exhaust gas from flowing back to the previous 180° exhaust cylinder; the intake valve opens earlier and the gas filling degree is more complete; through the exhaust gas in the combustion chamber High pressure and small amount of residual air; improve responsiveness; achieve higher torque at lower speed and higher boost pressure.

Volkswagen/Audi Variable Valve lift diagram

1-Large cam profile; 2-Small cam profile

3-Rolling rocker pawl; 4-Hydraulic lifter; 5-Valve guide

6-Exhaust valve; 7-piston; 8-large opening stroke

9-small opening stroke; 10-valve spring; 11-exhaust camshaft

Camshaft Construction

In order to switch between two different valve lifts on the exhaust camshaft, the camshaft is mountedEquipped with 4 movable cam pieces (with internal splines). Each cam piece is equipped with two pairs of cams with different cam lifts. The two lifts are switched through the actuator. The actuator engages the sliding groove on each cam member and moves the cam member on the camshaft. Each cam piece has two actuators for switching back and forth between the two lifts.

Spring-loaded balls in the camshaft lock the cam members at their respective ends Location. The sliding grooves and axial thrust bearings of the camshaft limit the movement of the cam member. The Volkswagen/Audi variable valve lift camshaft structure is shown in the figure below.

1-Removable cam piece; 2-Exhaust camshaft with external feather key;

3-With ball and spring locking cam members

Actuator

Actuator in two electrical With the assistance of the actuator (solenoid valve) [exhaust camshaft actuator (solenoid valve) A/B for cylinders 1 to 4], each cam member on the exhaust camshaft is pushed back and forth between the two switching positions. One actuator per cylinder switches to a greater valve lift and the other actuator switches to a smaller valve lift.

Each actuator is activated by a ground signal from the engine control unit. by mainThe relay provides the voltage. The current consumption of the actuator is about 3A. The position structure and principle of the actuator are as follows.

1-executor ( Solenoid valve); 2,10-metal pin; 3,6-reset slope;

4-movable cam piece; 5-exhaust camshaft; 7- Shell;

8-Electromagnetic coil; 9-Permanent magnet; 11-Conduit;

12-Permanent magnet; 13-Indented Metal pin; 14-Protruding metal pin

When current passes through the actuator When using an electromagnetic coil, the metal pin is moved within 18 to 22ms. The extended metal pin engages in the associated sliding groove of the cam member on the exhaust camshaft and pushes the sliding groove into the corresponding switching position through the rotation of the camshaft. The pin is mechanically retracted by a sliding groove (equivalent to a return ramp).

When the two actuators of the cam member are activated, only one actuator is always on The metal pin moves.

Camshaft position and switching when engine speed is low

The camshaft position and switching of the engine under lower speed load are shown in the figure below.