Engine retarder device having an opening-height variable exhaust valve

This invention discloses an engine reduction apparatus, characterized in that the discharging door open height of the reduction can be changed. The apparatus comprises driving piston, driving spring, spacing pin, one-way valve and corresponding oil channel, wherein the driving piston is used for controlling the non-locking of the discharging door, and using the non-locking to keep a opening degree of the discharging door; it also has a leakage passage, making the engine adjusting the throttle opening degree according to the rotary speed. When the engine operating in high speed, the throttle opening of the discharging door is large; and when operating in low speed, the throttle opening is small, by which the engine can emit proper brake force in every speed; besides, as the leakage passage, it can get lower engine height.