Patent ID: 8682535

Claim:
A vehicle speed estimator that estimates a vehicle speed of an all-wheel-drive construction vehicle, comprising: a rotation speed detector that detects a rotation speed of each of wheels at every predetermined time; and a reference wheel-speed calculator that selects a minimum rotation speed among the rotation speeds of the wheels detected by the rotation speed detector, calculates a reference wheel speed of the construction vehicle at every predetermined time, and output the reference wheel speed, wherein the reference wheel-speed calculator comprises: a minimum wheel-speed calculator that calculates a minimum wheel speed at every predetermined time based on the rotation speeds detected by the rotation speed detector; a variable filter processor that performs a low-pass filter processing to the minimum wheel speed calculated by the minimum wheel-speed calculator, the variable filter processor having a variable time constant; a time constant changer that changes the time constant of the variable filter processor in accordance with travel conditions of the construction vehicle; and a gear-shift state determiner that determines a state of a transmission of the construction vehicle, wherein the time constant changer comprises a gear-shift state time constant changer that increases the time constant of the variable filter processor when the gear-shift state determiner determines that the transmission is getting shifted.