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  • - [Narrator] You might have noticed

  • that after making a turn,

  • when you release the steering wheel

  • it will automatically return to the central position.

  • You will be amazed to find out

  • that this steering wheel return ability

  • is not achieved by any complicated mechanism

  • using springs or valves.

  • Instead, engineers have achieved

  • the return motion of the steering wheel

  • solely by giving the front wheels

  • an angle called a caster angle.

  • Let's discover the interesting physics

  • behind how providing an angle to the front wheels

  • makes the wheels and the steering wheel

  • come back to their original positions.

  • First, let's have a closer look

  • at the steering wheel mechanism.

  • It is clear that the rotation of the steering wheel

  • is transferred to the rack and pinion mechanism

  • which then turns both the wheels.

  • If you observe closely, you can see

  • that the wheels are turning along a particular axis.

  • This axis is called the steering axis.

  • In the current demonstration,

  • you can see that the steering axis is perfectly vertical.

  • However, this is not normally the case in practice.

  • In practice, the steering axis will be slightly inclined

  • to the vertical as shown.

  • This angle is called the caster angle.

  • You will get a clearer picture of this angle

  • when it is viewed from the side.

  • Let's watch how this steering mechanism works.

  • At first you might not notice much difference

  • from the previous mechanism.

  • However, when you understand

  • the concepts of patch area and pivot point,

  • you will notice a big difference.

  • Patch area is the area where force

  • is transferred to the wheels.

  • It is clear that the wheel is pivoted

  • to turn around at the meeting point

  • of the steering axle and road.

  • Let's call this meeting point the pivot point.

  • In the first mechanism,

  • the patch area is in line with the pivot point.

  • However, in the second case,

  • the patch area is way behind the pivot point.

  • To understand the effect of this trailing patch area,

  • let's study more about the forces

  • acting on the wheels during cornering.

  • Assume that your car is making a perfect circular turn

  • in a level plane.

  • To make this turn, what the car needs

  • is a centripetal force.

  • In a level plane turn, this centripetal force should come

  • from the frictional forces at the wheel patch area

  • and this fact is clear from this snapshot.

  • Now let's analyze in detail

  • what this frictional force does to the front wheels.

  • In the actual steering wheel geometry,

  • we saw that the patch area

  • is behind the steering axle meeting point or pivot point.

  • If you no longer hold the steering wheel

  • in this turned condition,

  • the effect of the centripetal force

  • on the wheels is obvious.

  • It will produce a restoring torque

  • and the wheels will automatically realign to the center.

  • Let's watch it from the top view also to get a better idea.

  • However, for the initial geometry

  • with zero caster angle,

  • there won't be any restoring torque

  • since the centripetal force passes through the pivot point.

  • In short, just by giving a positive caster angle

  • to the steering mechanism,

  • engineers were able to attain the restoring torque.

  • We salute the brilliant minds that visualized

  • such an ingenious idea and avoided the need

  • for a complex mechanism.

  • It is clear from these discussions

  • just how critical the caster angle is

  • for a vehicle's straight-line stability.

  • The caster angle is not adjustable on modern cars

  • but if during the wheel alignment operation

  • any variation is found,

  • due to wear and tear of the connected parts,

  • the issue should be fixed.

  • We hope you will support our educational services

  • on patreon.com

  • and don't forget to subscribe.

  • Thank you!

- [Narrator] You might have noticed

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B2 中上級

ステアリングホイールはどのようにして自動的にセンターに戻るのですか? (How does the Steering Wheel automatically returns to its center?)

  • 78 1
    OolongCha に公開 2021 年 01 月 14 日
動画の中の単語