Control device for hydraulically propelled work vehicle

Abstract

The current operational condition is discriminated as being the vehicle propulsion condition or the performing work condition. When the vehicle propulsion operational condition is discriminated, the maximum engine revolution speed is limited to a first revolution speed and the maximum displacement is limited to a first displacement value. When the performing work condition is discriminated, the maximum engine revolution speed is limited to a second revolution speed equal to or lower than the first revolution speed and the maximum displacement is limited to a second displacement value higher than the first displacement value. The first and second revolution speeds and the first and second displacement values are so determined that the first revolution speed multiplied by the first displacement value at least as relating to pressure for vehicle propulsion on level ground is less than the second revolution speed multiplied by the second displacement value as relating to the pressure for below the range of torque limitation control. By this, the pump output flow during vehicle propulsion on level ground is made lower than while performing work and, during vehicle propulsion, reduction of the pressure loss is made possible. Even with the identical pump pressure, the effective motor pressure is increased, so that its output torque can be increased. Because also the maximum displacement of the motor can be reduced according to the reduction of the maximum pump output flow amount, the construction of the hydraulic circuit can be made more compact.