STEERING SYSTEM - STRUCTURE AND OPERATING PRINCIPLE

2.2 STEERING UNIT

2.1.1. OPERATING PRINCIPLE

The turning force of the steering wheel (1) is transmitted through the handle shaft (2) to the handle shaft which is connected to the spline of the steering spool (7). The spool (7) is installed in the sleeve (4) which is installed in the steering unit housing (3). The spool (7) and sleeve (4) are fixed by the centering spring (6) and pin (5).

The pin hole (A) on the sleeve (4) is fit to the outer diameter of the pin (5), but the pin hole (B) on the spool (7) is larger than the outer diameter of the pin, holding the pin loosely. Therefore, the spool (7) rotates with the steering connecting shaft (2) simultaneously, but the sleeve rotates approx. 10° later than the spool. When the spool stops rotating, the sleeve stops after rotating the remainder of approx. 10°. This is because the spool and sleeve are fixed by the centering spring (6).

In other words, when the spool (7) and sleeve (4) are rotating clockwise or counterclockwise, being away from each other for approx. 10°, the oil hole for the left turn or the oil hole for the right turn is aligned to form the oil passage. When the spool (7) stops rotating and the sleeve (4) is returned to its original position (position relative to the spool) by the centering spring (6), the oil passage for the neutral position is formed.

One end of the drive shaft (8) is connected to the pin (5) through the spool (7) while its other end is connected to the Gerotor in the Gerotor pump (9). The Gerotor pump (9) is operated whenever the steering wheel is turned, and it is installed to the steering system to make manual steering possible in case of engine shut-off or gear pump malfunction.

STEERING SYSTEM - STRUCTURE AND OPERATING PRINCIPLE

2.3 OPERATING PRINCIPLE OF STEERING SYSTEM

This tractor has the full hydraulic, non-load reaction type steering system.

The full hydraulic type completely relies on hydraulic oil for transferring the power between the steering unit and the steering cylinder. It is not equipped with any mechanical transferring system, such as a drag link, pitman arm, rack or pinion. Therefore, the angles of the steering wheel and the front wheels may not agree to each other all the time.

For the load reaction type, when one steering cylinder is compressed by the outer force applied to the front wheel while driving, the returned oil turns the gerotor of the steering unit which then turns the steering wheel. Then, the oil flows to the other cylinder.

Therefore, when releasing the steering wheel after cornering, the steering wheel is automatically returned to the center position and the tractor moves straight forward or backward. On the other hand, for the non-load reaction type, when one steering cylinder is compressed and the tractor is turned, this turning angle cannot be maintained unless holding the steering wheel turned. The load reaction type is competitive for high-speed driving, but the steering wheel should be held to the desired angle to keep the steering angle, resulting in more noise and vibration compared to the non-load reaction type.