Crawler track tension adjusting device

1. A crawler track tension adjusting device for adjusting tension on a crawler belt of a crawler unit, the device comprising:

(a) a hydraulic actuator which is operable with operating oil to control the tension on the crawler belt, wherein an inflow of the operating oil to the hydraulic actuator is equal to an outflow of the hydraulic oil from the hydraulic actuator such that the hydraulic actuator is operable both in a direction to increase tension on the crawler belt and in a direction to decrease tension on the crawler belt under a same condition;

(b) an electric motor;

(c) a hydraulic pump driven by the electric motor;

(d) an operating condition detector which is disposed in a hydraulic circuit that connects the hydraulic pump to the hydraulic actuator, and which detects an operating condition of the hydraulic actuator; and

(e) a casing housing the hydraulic actuator, the electric motor, the hydraulic pump and the operating condition detector;

wherein the electric motor is controlled in accordance with a signal from the operating condition detector.

2. The crawler track tension adjusting device according to claim 1 , wherein the hydraulic actuator comprises a double rod cylinder that includes a cylinder, a piston slidable within the cylinder, and a piston rod including portions located respectively at front and rear ends of the piston.

3. The crawler track tension adjusting device according to claim 2 , wherein the piston rod portion located at the front end of the piston projects forward from the cylinder and is coupled to a yoke for supporting an idler about which the crawler belt is wound, and

wherein a pressure active area of a front pressure chamber located in front of the piston is equal to a pressure active area of a rear pressure chamber located behind the piston.

4. The crawler track tension adjusting device according to claim 1 , wherein the hydraulic pump comprises an operating oil tank integrally formed therewith.

5. The crawler track tension adjusting device according to claim 1 , further comprising:

an electromagnetic direction selector valve disposed in the hydraulic circuit in an oil line which connects the hydraulic pump to the hydraulic actuator,

wherein the operating condition detector comprises a hydraulic sensor disposed in a portion of the oil line which connects the direction selector valve to the hydraulic actuator, and

wherein in response to a signal from the hydraulic sensor, a controller controls the electric motor and the direction selector valve.

6. The crawler track tension adjusting device according to claim 5 , wherein the hydraulic circuit including the hydraulic actuator, the direction selector valve and the hydraulic pump has a hermetically closed structure.

7. The crawler track tension adjusting device according to claim 5 , wherein the hydraulic pump comprises an operating oil tank integrally formed therewith.

8. The crawler track tension adjusting device according to claim 5 , wherein the hydraulic actuator comprises a double rod cylinder that includes a cylinder, a piston slidable within the cylinder, and a piston rod including portions located respectively at front and rear ends of the piston,

wherein the piston rod portion located at the front end of the piston projects forward from the cylinder and is coupled to a yoke for supporting an idler about which the crawler belt is wound,

wherein a stroke sensor which detects a position of the piston rod faces the rear end of the piston rod, and

wherein a positional signal issued by the stroke sensor is input to the controller.

9. The crawler track tension adjusting device according to claim 1 , wherein said hydraulic pump comprises a bidirectional pump,

wherein the operating condition detector comprises a hydraulic sensor disposed in an oil line which connects said hydraulic pump to the hydraulic actuator, and

wherein a controller controls the electric motor in response to a signal from the hydraulic sensor.

10. The crawler track tension adjusting device according to any one of claims 1 to 4 , wherein two said casings are symmetrically disposed within respective track frames for respectively supporting crawler units disposed at right and left sides of a vehicle.

11. The crawler track tension adjusting device according to claim 9 , wherein two said casings are symmetrically disposed within respective track frames for respectively supporting crawler units disposed at right and left sides of a vehicle.

12. A crawler track tension adjusting device for adjusting tension on a crawler belt of a crawler unit, the device comprising:

(a) a hydraulic actuator which is operable with operating oil to control the tension on the crawler belt, wherein an inflow of the operating oil to the hydraulic actuator is equal to an outflow of the hydraulic oil from the hydraulic actuator such that the hydraulic actuator is operable both in a direction to increase tension on the crawler belt and in a direction to decrease tension on the crawler belt under a same condition;

(b) an electric motor;

(c) an operating oil tank storing operating oil;

(d) a hydraulic pump driven by the electric motor;

(e) an operating condition detector which is disposed in a hydraulic circuit that connects the hydraulic pump to the hydraulic actuator, and which detects an operating condition of the hydraulic actuator; and

(f) a casing housing the hydraulic actuator, the electric motor, the operating oil tank, the hydraulic pump and the operating condition detector; wherein the electric motor is controlled in accordance with a signal from the operating condition detector.