Up to now application of retarder to the heavy and medium vehicles an an auxiliary braking apparatus has been paid more attention by many researchers. To the vehicles usually running on the highland or in the city which make continual use of braking system, a set of assistant braking system can help a lot. This assistant system is able to augment steering capability excellently, improve comfort for passengers obviously and prolong the use limit of transmission and braking system. On flat road, the d...