Steering design — why use a worm gear instead of a spur pinion in some steering boxes? In steering gearboxes that use a worm mechanism (e.g., worm-and-sector or recirculating-ball types), what is the principal advantage compared with a simple spur pinion regarding driver feedback and disturbances at large steering angles?

Introduction / Context:
Automotive steering systems historically used worm-and-sector, worm-and-roller, or recirculating-ball mechanisms before widespread adoption of rack-and-pinion in passenger cars. The worm form provides mechanical characteristics that influence driver feel, back-drive sensitivity, and durability, particularly important for heavy vehicles and rough roads.

Given Data / Assumptions:

• Comparison is conceptual: worm-type steering box vs. pinion-type.
• Concern is driver feedback and disturbance rejection (kick-back) at larger lock angles.
• No power assist or EPS effects considered.

Concept / Approach:
Worm gears can be designed to be partly non-backdrivable due to their sliding contact and geometry, which reduces the transmission of road shocks back through the steering wheel. The effective friction and helix angle mean torque from the road wheels is less able to drive the worm backwards, thus limiting kick-back. This is valuable on uneven surfaces and with high front-axle loads.

Step-by-Step Solution:

Verification / Alternative check:
Heavy commercial vehicles and some off-road applications still use worm-type boxes for robustness and reduced feedback, even with power assistance.

Why Other Options Are Wrong:

• Improved comfort for tiny corrections: not the main differentiator; friction can even reduce light feel.
• Larger steering wheel angle without ratio change: wording is contradictory; ratio defines angle relationship.
• More responsive: worm boxes are generally less directly responsive than rack-and-pinion due to friction and compliance.
• Increased ratio without size change: ratio selection depends on gear geometry and package; not a universal advantage.

Common Pitfalls:
Confusing rack-and-pinion (spur pinion) with worm systems; assuming all steering feedback is beneficial when excessive kick-back is hazardous.

Final Answer: