In machine kinematics for automobile systems, an automobile steering gear (e.g., Ackermann steering linkage used to turn the front wheels) is classified as which type of kinematic pair arrangement, considering the nature of contacts at its joints and links?

Introduction / Context

Automobile steering mechanisms (such as the Ackermann steering gear) are linkage systems designed to guide the front wheels so that they approximately roll about a common instantaneous center during a turn. Classifying these mechanisms into lower or higher pairs helps in understanding contact types, wear behavior, and manufacturability of the joints.

Given Data / Assumptions

• Typical passenger-car steering linkages with pins/ball joints connecting levers and arms.
• Ideal kinematic modeling (small clearances, lubricated joints).
• Focus on the contact nature between mating elements.

Concept / Approach

Kinematic pairs are grouped by how mating elements touch. Lower pairs exhibit surface contact (e.g., a pin in a hole—turning pair; a slider in a guide—sliding pair), while higher pairs exhibit line/point contact (e.g., cam–follower, gear teeth, pure rolling). Steering linkages employ revolute (pin) joints—textbook examples of lower pairs—because they provide robust constraint with distributed (surface) contact areas, minimizing contact stress compared with point/line contact.

Step-by-Step Solution

Verification / Alternative check

Standard kinematics texts classify four-bar linkages, steering linkages, and slider–crank joints as lower-pair mechanisms. Higher pairs are reserved for cams, gears, and rolling contacts.

Why Other Options Are Wrong

• Higher pair: implies line/point contact (cams/gears), which is not the dominant joint type in Ackermann steering.
• Sliding pair: a steering linkage primarily uses turning (revolute) joints, not long-stroke sliders.
• Rolling pair: pure rolling contacts are not the basis of the linkage joints.
• Cam (point/line contact) pair: not present in standard linkage steering.

Common Pitfalls

• Confusing the term “steering gear” with a rack-and-pinion gear set; the linkage mechanism classification still depends on its revolute joints, i.e., lower pairs.

Final Answer

lower pair