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Definition
The worm and sector steering gearbox is one of the earliest types of steering gear mechanisms.
It converts the rotary motion of the steering wheel into the angular motion of the road wheels using a worm gear and a sector gear.
Components of worm and sector steering box:
A worm and sector steering gear consists of the following main components:
- Worm Gear (or Worm Shaft):
- Connected to the steering wheel.
- A screw-like gear that rotates when the driver turns the steering wheel.
- Sector Gear:
- A partial gear (a “sector” of a full gear) with teeth cut on its periphery.
- It meshes with the worm gear.
- Mounted on the sector shaft (or cross shaft), which is connected to the pitman arm.
- Pitman Arm:
- Transfers motion from the sector shaft to the steering linkage (drag link, tie rods, etc.).
- Housing:
- Encloses and supports all the components.
- Filled with lubricant to reduce friction.
Working Principle of worm and sector steering box:
- When the steering wheel is rotated, the worm gear rotates.
- The worm gear teeth push against the teeth of the sector gear.
- The sector gear rotates about its pivot, which moves the pitman arm.
- The pitman arm moves the drag link and tie rods, turning the front wheels left or right.
Advantages of worm and sector steering box:
- Simple and cheap design – easy to manufacture.
- Durable – can handle rough road conditions.
- Suitable for low-speed vehicles and trucks.
Disadvantages of worm and sector steering box:
- More friction and backlash compared to modern systems.
- Steering effort is higher – more force is required by the driver.
- Limited steering precision.
Applications
- Widely used in older trucks, buses, and cars before the development of more advanced steering gear mechanisms.
- Still found in some heavy-duty commercial vehicles because of its strength.
FAQ Section:
1. What is a worm and sector steering gearbox?
It is a type of manual steering mechanism that uses a worm gear connected to the steering wheel and a sector gear connected to the pitman arm to transmit motion to the wheels.
2. Where is worm and sector steering commonly used?
It was widely used in older cars, trucks, and buses. Today, it is mostly found in heavy-duty vehicles where high strength and durability are required.
3. How does a worm and sector steering gearbox work?
When the driver rotates the steering wheel, the worm gear turns and engages with the sector gear, causing it to rotate and move the pitman arm, which turns the front wheels.
4. What are the main components of a worm and sector steering system?
- Steering wheel
- Worm gear (on the steering shaft)
- Sector gear
- Pitman arm
- Steering gearbox housing
5. What is the advantage of worm and sector steering?
It is simple, strong, and inexpensive to manufacture. It is capable of handling large steering loads, making it suitable for heavy vehicles.
6. What is the main disadvantage of worm and sector steering?
It has more friction and backlash compared to modern steering systems like rack-and-pinion, leading to less precise steering and more driver effort.
7. What is backlash in worm and sector steering?
Backlash is the slight free play or looseness between the worm and sector gear teeth, which can make the steering feel less responsive.
8. How can backlash be reduced in a worm and sector system?
It can be minimized by proper adjustment of the sector gear mesh and maintaining proper lubrication inside the gearbox.
9. Does worm and sector steering require lubrication?
Yes. The gearbox housing is filled with grease or oil to reduce friction, prevent wear, and ensure smooth operation.
10. Why is worm and sector steering not common in modern cars?
Modern vehicles use rack-and-pinion or recirculating ball steering because they provide better steering precision, lower friction, and require less driver effort.
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