Patent ID: 7240489

Claim:
A drive system of a working vehicle comprising: a main engine drivingly connected to a hydraulic pump having a displacement volume that is variable by a pump actuator, the hydraulic pump is drivingly connected to a first hydraulic motor that is drivingly connected to a first wheel engaging the ground, the first hydraulic motor having a variable displacement volume by means of a first actuator, the hydraulic pump is also connected to a second hydraulic motor that is drivingly connected to a second wheel engaging the ground, the second hydraulic motor having a variable displacement volume by means of a second actuator; a control device is coupled to a sensor configured to sense the position of a control lever for setting rotational speed of the first and second wheels, the control device is further connected to the first and second actuators and configured to adjust the first and second actuators in response to movement of the control lever; and the control device being configured to adjust the first actuator to reduce the displacement volume of the first hydraulic motor and reduce the rotational speed of the first wheel when an undesirable operating condition is detected at the first wheel, the control device also being configured to shift the second actuator and the pump actuator to maintain a constant speed of travel by shifting the second actuator toward a greater displacement volume up to a maximum displacement volume and shifting the pump actuator toward a reduced displacement volume if and only if the shifting of the second actuator is insufficient to compensate for the change in the displacement volume of the first hydraulic motor.