Steering system of industrial machine and method of changing body-articulating angle

1. A steering system for an industrial machine comprising:

a body-articulating angle changing means for changing a body-articulating angle of the industrial machine, by receiving and discharging pressurized oil;

first and second steering means provided in the industrial machine and operated by an operator;

a first signal pressure output means for outputting a first signal pressure mechanically responsively to an operation of the first steering means;

a second signal pressure output means for outputting a second signal pressure mechanically responsively to an operation of the second steering means;

a third signal pressure output means which selects whether or not the third signal pressure output means outputs a third signal pressure, in response to the second signal pressure fed to the third signal pressure output means; and

feeding and discharging control means coupled to the first signal pressure output means and to the third signal pressure output means. for controlling feeding and discharging of the pressurized oil with respect to the body-articulating angle changing means, based on the first signal pressure or the third signal pressure fed to the feeding and discharging control means;

wherein in a state where the first steering means is operated, the first signal pressure output means outputs the first signal pressure, while the third signal pressure output means stops outputting of the third signal pressure regardless of whether the second signal pressure is fed to the third signal pressure output means, and the feeding and discharging control means operates based on the first signal pressure fed to the feeding and discharging control means.

2. The steering system for an industrial machine according to Claim 1 ,

wherein the first steering means is a rotatable steering wheel;

the first signal pressure output means is a power steering unit which is mechanically coupled to the steering wheel and is operative in response to a rotational operation of the steering wheel; and

the power steering unit outputs the first signal pressure according to a direction in which the steering wheel is rotated and a rotational operation position of the steering wheel.

3. The steering system for an industrial machine according to claim 1 ,

wherein the second steering means is a steering lever which is capable of being tilted;

the second signal pressure output means is a pilot valve which is mechanically coupled to the steering lever and is operative in response to a tilting operation of the steering lever; and

the pilot valve outputs the second signal pressure according to a direction in which the steering lever is tilted and a tilting operation position of the steering lever.

4. The steering system for an industrial machine according to claim 1 ,

wherein the third signal pressure output means includes:

a first switching valve which switches a valve position from a position in which the pressurized oil is blocked by the first switching valve to a position in which the pressurized oil outflows from the first switching valve, in response to the second signal pressure fed to the first switching valve; and

a second switching valve which switches a valve position between a first position in which the pressurized oil outflowing from the first switching valve is returned to a tank and a second position in which the pressurized oil is output as the third signal pressure;

wherein in a state where the first steering means is operated, the second switching valve is placed in the first position.

5. The steering system for an industrial machine according to claim 1 ,

wherein the third signal pressure output means includes:

a first switching valve which switches a valve position from a position in which the pressurized oil is blocked by the first switching valve to a position in which the pressurized oil outflows from the first switching valve, in response to the second signal pressure fed to the first switching valve; and

a second switching valve which switches a valve position between a first position in which the pressurized oil outflowing from the first switching valve is blocked by the second switching valve and a second position in which the pressurized oil is output as the third signal pressure;

wherein in a state where the first steering means is operated, the second switching valve is placed in the first position.

6. The steering system for an industrial machine according to claim 4 , further comprising:

a switching operation means for selecting whether a steering operation of the second steering means is enabled or disenabled;

wherein in a state where the switching operation means is operated to enable the steering operation of the second steering means, the valve position of the second switching valve is normally the second position and switches from the second position to the first position, when the first steering means is operated; and

wherein in a state where the switching operation means is operated to disenable the steering operation of the second steering means, the valve position of the second switching valve is the first position.

7. The steering system for an industrial machine according claim 4 , wherein

the first signal pressure output means outputs a detection signal pressure which branches from the first signal pressure in a state where the first steering means is operated, and stops outputting of the detection signal pressure in a state where the first steering means is not operated, and

the second switching valve switches the valve position from the second position to the first position, in response to the detection signal pressure fed to the second switching valve.

8. A method of changing a body-articulating angle of an industrial machine including first and second steering means operated by an operator, comprising the steps of:

outputting a first signal pressure mechanically responsively to an operation of the first steering means;

outputting a second signal pressure mechanically responsively to an operation of the second steering means;

selecting whether or not to output a third signal pressure in response to the second signal pressure; and

controlling the body-articulating angle of the industrial machine based on the first signal pressure or the third signal pressure, by a feeding and discharging control means coupled to a first signal pressure output means for outputting the first signal pressure and to a third signal pressure output means for outputting the third signal pressure;

wherein in a state where the first steering means is operated, outputting of the third signal pressure is stopped, regardless of whether or not the second signal pressure is fed, in the selecting step; and

in a state where the first steering means is operated, the body-articulating angle is controlled based on the first signal pressure, in the step of controlling the body-articulating angle.