Wheel driving device and wheel driving method for hybrid construction machine
The present disclosure relates to a wheel driving device and a wheel driving method for a hybrid construction machine, in which in a construction machine having wheels, particularly, a hybrid wheel loader, by small-capacity low-speed electric motors, small-capacity high-speed electric motors, transmissions each having a clutch, and a control unit which are installed for all of the wheels each, the wheel driving device drives the low-speed electric motor during low-speed driving and drives the high-speed electric motor during high-speed driving by turning on and off the clutch during the low-speed driving and the high-speed driving, thereby reducing manufacturing costs of the wheel driving device, improving fuel economy of the construction machine, reducing abrasion of tires mounted on the wheels, improving durability of the tires, and ensuring traveling stability.
1. A wheel driving device for a hybrid construction machine, which includes an engine which generates power, a motor generator which is connected to the engine and generates electrical energy, an electricity storage unit which is electrically connected to the motor generator, inverters which are connected to the electricity storage unit, and a plurality of wheels, the wheel driving device comprising:
a plurality of first electric motors each of which is connected to each of the plurality of wheels and electrically connected to each of the inverters;
a plurality of second electric motors each of which is connected to each of the plurality of wheels in parallel with the each of the plurality of first electric motors and electrically connected to each of the inverters;
transmissions each of which has one side connected to each of the plurality of wheels, and the other side connected to each of the first electric motors and each of the second electric motors; and
a control unit which controls transmission of driving power from the first electric motors and the second electric motors to the plurality of wheels via the transmission,
wherein each of the transmissions includes a first speed reducer which is connected to both of the first electric motor and the second electric motor and reduces a rotational speed of the first electric motor or a rotational speed of the second electric motor,
wherein each of the transmissions includes a clutch which is installed between the first speed reducer and the first electric motor and permits or cuts off power transmission from the first electric motor to the plurality of wheels, and
wherein the control unit includes:
a permissible RPM data storage unit which stores permissible RPM data of the first electric motor and the second electric motor;
a permissible torque data storage unit which stores permissible torque data of the first electric motor and the second electric motor;
a data receiving unit which receives data related to current RPM and current torque of the first electric motor or the second electric motor;
a comparison unit which compares the permissible RPM and the permissible torque of the first electric motor and the second electric motor, which are stored in the permissible RPM data storage unit and the permissible torque data storage unit, with the current RPM and the current torque of the first electric motor or the second electric motor which are received by the data receiving unit; and
a controller which controls on/off control for the clutch so as to drive the second electric motor by turning off the clutch when the current torque of the first electric motor is lower than the permissible torque as a result of the comparison by the comparison unit, and to drive the first electric motor by turning on the clutch when the current RPM of the second electric motor is equal to or lower than the permissible RPM.
2. The wheel driving device of claim 1 , wherein each of the transmissions includes:
a second speed reducer which is connected to the first electric motor and located between the first electric motor and the clutch wherein the second speed reducer reduces a rotational speed of the first electric motor.
3. The wheel driving device of claim 1 , wherein the control unit controls to drive the first electric motors during a first speed driving, and controls to drive the second electric motors during a second speed driving.
4. The wheel driving device of claim 1 , wherein the control unit controls to drive both of the first electric motors and the second electric motors together during a first speed driving.
5. The wheel driving device of claim 1 , further comprising:
a speed increaser which is installed between the engine and the motor generator.
6. The wheel driving device of claim 1 , wherein each of the inverters is separately installed to each of the first electric motors and to each of the second electric motors, respectively.
7. The wheel driving device of claim 2 , wherein the first electric motor and the second electric motor have the same electric motor capacity, and a reduction ratio of the second speed reducer is 3:1.
8. A wheel driving device for a hybrid construction machine, which includes an engine which generates power, a motor generator which is connected to the engine and generates electrical energy, an electricity storage unit which is electrically connected to the motor generator, inverters which are connected to the electricity storage unit, and a plurality of wheels, the wheel driving device comprising:
a plurality of first electric motors each of which is connected to each of the plurality of wheels and electrically connected to each of the inverters;
a plurality of second electric motors each of which is connected to each of the plurality of wheels in parallel with the each of the plurality of first electric motors and electrically connected to each of the inverters;
transmissions each of which has one side connected to each of the plurality of wheels, and the other side connected to each of the first electric motors and each of the second electric motors;
a first speed reducer which is connected to both of the first electric motor and the second electric motor and reduces a rotational speed of the first electric motor or a rotational speed of the second electric motor;
a second speed reducer which is connected to the first electric motor and reduces a rotational speed of the first electric motor;
a clutch which is installed between the first speed reducer and the second speed reducer, and permits or cuts off power transmission from the first electric motor to the plurality of wheels; and
a control unit which controls transmission of driving power from the first electric motors and the second electric motors to the plurality of wheels via the transmission,
wherein the first electric motor and the second electric motor have the same electric motor capacity, and a reduction ratio of the second speed reducer is 3:1.