Module 1. Tractor Mechanics
Module 2. Traction
Module 3. Introduction to Transmission System
Module 4. Clutch System
Module 5. Gear Box
Module 6. Differential and Final drive
Module 7. Brakes
Module 8. Steering system
Module 9. Hydraulics
Module 10. Power Transmission
Module 11. Human Factors
Lesson 25. Steering linkage. Types of steering gear (steering box)
One of the important human interface system in the automobile is the steering gear. The steering gear is a device for converting the rotary motion of the steering wheel into straight line motion of the linkage. The steering gears are enclosed in a box, called the steering gear box. The steering wheel is connected directly to the steering linkage it would require a great effort to move the front wheels. Therefore to assist the driver, a reduction system is used.
The different types of steering gears are as follows:
1. Worm and sector steering gear.
2. Worm and roller steering gear.
3. Cam and double lever steering gear.
4. Worm and ball bearing nut steering gear.
5. Cam and roller steering gear.
6. Cam and peg steering gear.
7. Recirculating ball nut steering gear.
8. Rack and pinion steering gear.
Recirculating ball steering gear
This is the most common steering gear in Indian tractors. In this the lower end of the steering column has a worm. A box type nut is clamped on this worm which has numerous ball bearings circulating between the worn and the nut. As the steering wheel on top of the steering column is turned, the nut moves up and down. This movement of the nut is sensed by the sector of the pitman which is connected to the nut. The movement of the nut is transferred into the rotational motion of the pitman. Drop arms are mounted on this pitman shafts. The blow-up figure of a recirculating ball steering box is as shown in Fig 25.1.
Worm and Roller Type Steering Box
In case of worm and roller steering, the worm at the lower end of the steering column is in the form of a cam. There is a roller which follows the shape of the worm. The roller is a part of the pitman. As the roller follows the cam when the steering column is turned, the motion is transferred to the pitman and to the drop arms. An exploded view of the worm and nut steering is given in Fig. 25.2
Worm and Sector Type Steering Box
In this type of steering box, the steering worm of the steering column rotates a steering gear sector which is meshed with the worm. The gear sector in turn rotates the pitman on which it is mounted. The pitman is further connected to the steering linkage for steering the wheels. The Fig 25.3 shows the method in which the worm and sector steering is used to convert the rotation of steering column into rotation of pitman.
Rack and Pinion Type Steering Box
In a rack and pinion steering gear, a pinion is attached at the end of the steering shaft. When the steering wheel is turned, the pinion gear spins, moving the rack – left or right, depending on which way the steering is turned. The rack forms the part of the tie rod with steering spindle at its ends which push or pull the steering links for steering the wheels. Fig 25.4 shows the arrangement for a rack and pinion steering box
The recirculating ball mechanism has the advantage of a much greater mechanical advantage, so that it was found on heavier vehicles while the rack and pinion was originally limited to smaller and lighter ones.