Turning control system for use in a track-laying vehicle

A turning control system for use in a track-laying vehicle comprising:

• (a) a power source for generating a rotary driving force;
• (b) a non-stage transmission which transmits rotary driving force from the power source such that crawler belts provided at both sides of the vehicle travel at the same speed in the same direction, thereby driving the vehicle forwards or backwards;
• (c) transmission revolution speed ratio detector means for detecting an actual transmission revolution speed ratio at the time of transmission of rotary driving force from the power source through the non-stage transmission;
• (d) a steering motor which is driven by the power source, for driving the crawler belts such that a relative travel difference results between the crawler belts, thereby turning the vehicle rightwards or leftwards;
• (e) steering instructing means which can be displaced from a neutral position by operation and which instructs, in accordance with the displacement direction and displacement distance of the steering instructing means, a turning direction and a turning radius for the vehicle, the turning radius decreasing as the displacement distance increases;
• (f) displacement detector means for detecting the displacement of the steering instructing means;
• (g) target steering motor speed ratio setting means for setting a target steering motor speed ratio based on the displacement of the steering instructing means detected by the displacement detector means, the target steering motor speed ratio being the ratio of a revolution speed of the steering motor to a revolution speed of the power source;
• and
• (h) steering motor revolution speed control means for controlling the revolution speed of the steering motor such that the target steering motor speed ratio set by the target steering motor speed ratio setting means becomes proportional to the actual transmission revolution speed ratio detected by the transmission revolution speed ratio detector means at least in the region of low vehicle speeds, when the steering instructing means is displaced and kept in a certain position and therefore there is no change in the displacement of the steering instructing means detected by the displacement detector means.