The hydraulic motor is mounted directly in the wheels' wheel hydraulic drive system "is an auxiliary hydraulic drive unit, roller hydraulic maintenance costs, it can solve engineering machinery need to improve traction, but can not use all-wheel drive, difficult to arrange traditional The problem of mechanical transmission. Variable speed hydraulic transmission performance between the different ways to make the drive wheels can be coordinated simultaneously, Hanzhong roller hydraulic maintenance, which can also be seen as a power split transmission, in a sense: the power machine power is allocated to several set wheels on the ground after coupling produces traction propel the vehicle movement. Currently, many construction machinery manufacturers will use this technology for a partial self-propelled drive capability, such as the self-propelled graders and scrapers such machinery. Secondary regulation hydrostatic transmission compared with conventional hydrostatic transmission, the advantage is more easy to control, can work in four quadrants, can not change the circumstances under forms of energy to recover energy, roller hydraulic repair companies, the energy of storage, accelerate the use of hydraulic accumulators can greatly improve the accelerating power, hydraulic roller maintenance organizations, and the system is no pressure peak, as the primary element and the secondary element mounted separately, available oil source to a plurality of hydraulic power element by a pumping station , reducing cooling costs, reduce the manufacturing cost of the apparatus, high system efficiency.