Patent ID: 6938719

Claim:
A speed control system for a wheeled hydraulic traveling vehicle, comprising: a plurality of variable displacement hydraulic pumps respectively driven by a prime mover; a pump displacement regulation device that respectively regulates displacement amount of the hydraulic pumps; a variable displacement hydraulic motor for traveling driven by pressure oil discharged from the plurality of hydraulic pumps; a motor displacement regulation device that regulates a displacement amount of the hydraulic motor; a plurality of control valves, respectively provided in correspondence with the hydraulic pumps, that controls flow of the pressure oil supplied to the hydraulic motor from the hydraulic pumps in response to a travel control command; an ultra low speed command device that issues an ultra low speed travel signal for the wheeled hydraulic traveling vehicle to use an ultra low speed set as an upper limit; and a first ultra low speed control device that controls the motor displacement regulation device to set the displacement amount of the hydraulic motor to maximum, and also controls drive of the control valves to allow the pressure oil to flow from at least one of the plurality of hydraulic pumps to the hydraulic motor while preventing the pressure oil flowing from the remaining hydraulic pumps to the hydraulic motor, if the ultra low speed travel command is issued by the ultra low speed command device, wherein: when the ultra low speed travel signal is issued by the ultra low speed command device, the wheeled hydraulic traveling vehicle travels at a speed in accordance with an amount of depression of an accelerator pedal, with the upper limit of the speed being the ultra low speed.