Wheel driving system for construction machinery

1. A wheel driving system, comprising:

a generator connected to an engine and configured to generate electrical energy;

a front axle configured to drive at least one front wheel, and including a front electric motor configured to produce a driving torque from the electrical energy supplied from the generator and a front transmission configured to convert the driving torque into a conversion torque required according to a speed of construction machinery and transmit the conversion torque to the front wheel via a front drive shaft;

a rear axle configured to drive at least one rear wheel, and including a rear electric motor configured to produce a driving torque from the electrical energy supplied from the generator and a rear transmission configured to convert the driving torque into a conversion torque required according to the speed of the construction machinery and transmit the conversion torque to the rear wheel via a rear drive shaft; and

a central connection unit operatively connected to the front axle and the rear axle and configured to transmit the conversion torque between the front axle and the rear axle,

wherein at least one of the front wheel and the rear wheel comprises a left wheel and a right wheel,

wherein at least one of the front drive shaft and the rear drive shaft comprises a left drive shaft connected to the left wheel and a right drive shaft connected to the right wheel,

wherein at least one of the front transmission and the rear transmission comprises a left transmission and a right transmission,

wherein at least one of the front electric motor and the rear electric motor comprises a left electric motor connected to the left drive shaft via the left transmission and a right electric motor connected to the right drive shaft via the right transmission,

wherein the left drive shaft and the right drive shaft are connected to each other by a drive shaft connection unit, and

wherein the central connection unit is operatively connected to the drive shaft connection unit.

2. The wheel driving system of claim 1 , wherein the front transmission and the rear transmission have at least two speed steps, and the front transmission has a first shift ratio at a same speed step and the rear transmission has a second shift ratio different from the first shift ratio at the same speed step.

3. The wheel driving system of claim 2 , wherein the first shift ratio is greater than the second shift ratio.

4. The wheel driving system of claim 1 , wherein when the speed of the construction machinery reaches a first shift permissible speed, a speed step of the front transmission is shifted, and when the speed of the construction machinery reaches a second shift permissible speed different from the first shift permissible speed, a speed step of the rear transmission is shifted.

5. The wheel driving system of claim 1 , wherein the front transmission and the rear transmission have at least two speed steps, and when the speed of the construction machinery ranges between a first shift permissible speed and a second shift permissible speed, the speed step of the front transmission is different from the speed step of the rear transmission.

6. The wheel driving system of claim 1 , wherein the front drive shaft connection unit comprises a differential gear.

7. The wheel driving system of claim 1 , wherein the rear drive shaft connection unit comprises a differential gear.

8. A wheel driving system, comprising:

a generator connected to an engine and configured to generate electrical energy;

a front axle configured to drive at least one front wheel, and including a front electric motor configured to produce a driving torque from the electrical energy supplied from the generator and a front transmission configured to convert the driving torque into a conversion torque required according to a speed of construction machinery and transmit the conversion torque to the front wheel via a front drive shaft;

a rear axle configured to drive at least one rear wheel, and including a rear electric motor configured to produce a driving torque from the electrical energy supplied from the generator and a rear transmission configured to convert the driving torque into a conversion torque required according to the speed of the construction machinery and transmit the conversion torque to the rear wheel via a rear drive shaft; and

a central connection unit operatively connected to the front drive shaft and the rear drive shaft and configured to transmit the conversion torque between the front axle and the rear axle,

wherein the front transmission and the rear transmission have at least two speed steps, and

wherein when the speed of the construction machinery reaches a first shift permissible speed, a speed step of the front transmission is shifted from a first speed step to a second speed step, and when the speed of the construction machinery reaches a second shift permissible speed greater than the first shift permissible speed, a speed step of the rear transmission is shifted from a first speed step to a second speed step.

9. The wheel driving system of claim 8 , comprising:

wherein when the speed of the construction machinery ranges between the first shift permissible speed and the second shift permissible speed, the speed step of the front transmission is different from the speed step of the rear transmission.