Gearshift controller for industrial vehicle

1. A gearshift controller for an industrial vehicle, comprising:

a speed ratio detection unit that detects a speed ratio of speed of an input axis and of an output axis of a torque converter;

a gearshift control unit that shifts up a speed stage when the detected speed ratio is equal to or more than a first predetermined value and shifts down the speed stage when the detected speed ratio is equal to or less than a second predetermined value, which is smaller than the first predetermined value; and

an operation member with which a downshift to the first speed is instructed by operation thereof by an operator, wherein

when the downshift is instructed by the operation member, the gearshift control unit controls the speed stage to be kept at the first speed for a predetermined time period regardless of the speed ratio detected by the speed ratio detection unit, and

the gearshift control unit allows switching to the first speed by operation of the operation member while the vehicle is traveling at a second speed and prohibits the switching to the first speed by operation of the operation member while the vehicle is traveling at a third or higher speed.

2. A gearshift controller for an industrial vehicle according to claim 1 , wherein

when the downshift is not instructed with the operation member, the gearshift control unit controls a minimum speed stage while the vehicle is traveling to be kept at a second speed.

3. A gearshift controller for an industrial vehicle according to claim 1 , further comprising:

a speed stage setting unit that sets a maximum speed stage of the transmission with operation by the operator and wherein

the gearshift control unit limits the speed stage equal to or lower than the set maximum speed stage upon the upshift.

4. A gearshift controller for an industrial vehicle according to claim 1 , wherein

the operation member is disposed to an operation member for working that operates an actuator for working or in the vicinity of the operation member for working.

5. An industrial vehicle comprising:

four tires;

a body comprising a front side frame and a rear side frame articulately connected to each other, the body being supported by the tires;

a cab provided in front of the rear side frame;

an engine compartment provided in rear of the rear side frame;

an arm provided rotatably in a vertical direction with respect to the front side frame;

a bucket provided rotatably at a top of the arm; and

a gearshift controller according to claim 1 .

6. A gearshift controller for an industrial vehicle, comprising:

a rotational speed detection unit that detects respective rotational speeds of an input axis and of an output axis of a torque converter;

a solenoid control unit that drives a solenoid for gearshift of a transmission;

a gearshift control unit having an input unit that inputs signals detected by the rotational speed detection unit and a calculation unit that calculates a speed ratio of rotational speeds of the input axis and of the output axis based on the signals input by the input unit, the gearshift control unit shifting up a speed stage when the calculated ratio of speeds is equal to or more than a first predetermined value and shifting down the speed stage when the calculated ratio of speeds is equal to or less than a second predetermined value, which is smaller than the first predetermined value; and

an operation member with which a downshift to the first speed is instructed by operation thereof by an operator, wherein

the gearshift control unit further includes

a memory unit in which there is set a predetermined time period longer than a standard time period required for the vehicle to thrust into earth and sand after the downshift of the speed stage to the first stage upon excavation; and

an output unit that outputs a control signal to the solenoid control unit so as to control the speed stage to be maintained at the first speed for the predetermined time period regardless of the calculated ratio of speeds when the downshift of the speed stage to the first speed is instructed with the operation member, wherein

the gearshift control unit allows switching to the first speed by operation of the operation member while the vehicle is traveling at a second speed and prohibits the switching to the first speed by operation of the operation member while the vehicle is traveling at a third or higher speed.