Weichai Power Safety Brake System-WEVB is a patented technology purchased by Weichai Power from MAN, Germany. This technology is already a standard configuration for heavy trucks in developed countries and has become a mandatory structure for use by regulations.

The main function of this mechanism is to increase the braking torque generated by the diesel engine when the truck needs to decelerate, so that the vehicle continuously reduces or stabilizes the vehicle speed, effectively improves the control performance of the vehicle, can ensure the safety of the vehicle on the downhill road in the mountain, and reduces the brake The frequency of use of the system reduces the degree of wear of the braking system, reduces the operating cost of the vehicle, and improves the economy of use. The driver does not need or can reduce the watering and cooling of the tires on the downhill road. The number of brakings is greatly reduced, reducing the labor intensity of driving. Increased driving comfort.

The traditional exhaust brake device adopts a butterfly valve switch to close the exhaust pipe channel, so that the piston is subjected to the back pressure of the gas during the exhaust stroke, which prevents the engine from running and produces a braking effect, so as to achieve the purpose of controlling the vehicle speed.

WEVB exhaust valve braking is based on the traditional butterfly valve exhaust auxiliary braking device. When the butterfly throttle valve is closed, the diesel engine works like a compressor under the drag of the car's gravity. The pressure of the exhaust gas in the exhaust channel rises sharply. The pressure wave generated by the exhaust gas of the adjacent cylinder will cause it to be under the intake stroke The exhaust valve of the cylinder near the dead center opens uncontrollably.

The exhaust valve braking device (EVB) uses the phenomenon that the exhaust valve is automatically opened by the pressure wave during the braking process. By adding a set of actuators to control the exhaust valve stroke, the exhaust valve is realized during the engine braking process Keep a gap open to improve engine braking efficiency.

When the exhaust valve is opened by the pressure wave, the small piston in the exhaust valve brake mechanism follows the exhaust valve downward due to its own weight and the action of the spring. At this time, the check valve opens, filling the cavity above the small piston Oil, and because in the above process and the subsequent compression and power strokes, the oil seal plane of the exhaust valve rocker arm is close to the oil seal surface of the oil seal screw, the oil discharge hole is closed, so the sealed oil above the small piston The small piston cannot be retracted into the rocker arm, forcing the exhaust valve to be in an open state, and the stroke of compression and power stroke is maintained at about 1-2mm afterwards. At the beginning of the exhaust stroke, the exhaust valve is fully opened by the movement of the rocker arm, the oil discharge hole on the exhaust valve rocker arm is opened, the lubricating oil is sprayed out, and the extended small piston returns to position under the valve pressure.

The above process is repeated cyclically, thereby increasing the braking power of the diesel engine. When the intake stroke, compression stroke, power stroke, exhaust stroke, butterfly valve is closed, the exhaust valve is opened by a pressure wave from the exhaust pipe to a gap, the check valve in the rocker arm of the exhaust valve opens, and the lubrication in the oil hole of the rocker arm The oil fills the cavity above the small piston. The closed engine oil prevents the small piston from retracting into the rocker arm, forcing the opened exhaust valve to maintain an opening of approximately 1-2 mm.

The gap is always maintained, and compressed air is discharged to the exhaust pipe through the throttling action, so that the gas pressure in the cylinder is significantly reduced at the end of compression. The piston descends, and the vacuum generated by the gas is drawn from the exhaust pipe into the cylinder. Also due to the throttling effect, the pressure of the gas in the cylinder is further reduced, thereby avoiding the compression work driving the engine to do positive work. This stroke is caused by the exhaust valve being cam The shaft opens, the drain hole at the top of the rocker arm is also opened, the lubricant is drained, the small piston returns to the position under the pressure of the valve, the opened small gap is closed, and one cycle is completed.