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    the ackerman steering gear mechanism is preferred to the davis steering gear mechanism, because

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    KOM – Unit 3 – Question Bank Answers – R. Syam Sudhakar Rao

    KOM – Unit 3 – Question Bank Answers

    1. What is an automobile steering gear? What are its types? Which steering gear is preferred and why? (MAY/JUNE 2019[R16])Ans:Steering gear mechanism: The steering gear mechanism is used for changing the direction of two or more of the wheel axles. with reference to the chassis, so as to move the automobile in any desired path.Types of Steering gears: There are two steering gears commonly used in automobiles.

    Davis steering gear

    Ackerman steering gear

    Ackerman steering gear is preferred, because the Davis steering has sliding pairs, whereas the Ackermann steering has only turning pairs. The sliding pair has more friction than the turning pair, therefore, the Davis steering gear will wear out earlier and become inaccurate after certain time. Hence Davis steering gear is not in common use.

    2. Derive the condition for correct steering of an automobile? (MAY/JUNE 2019[R16])Ans: In order to avoid skidding in automobiles when the vehicle take a turn, the two front wheels must turn about the same instantaneous centre which lies on the axis of the back wheels. If the instantaneous centre of the two front wheels do not coincide with the instantaneous centre of the back wheels, the skidding on the front or back wheels will definitely take place, which will cause more wear and tear of the tyres.

    The condition for correct steering is that all the four wheels must turn about the same instantaneous centre.

    The axis of the inner wheel makes a larger turning angle θ than the angle Φ subtended by the axis of outer wheel.

    Let a = wheel track b = wheel base

    c = distance between the pivots A and B of the front axle

    Now from triangle IBP,

    cot θ = BP/IP

    and from triangle IAP,

    cot Φ = AP/IP = (AB+BP)/IP = (AB/IP) + (BP/IP) = c/b + cot θ

    ∴ cot Φ – cot θ = c/b

    This is the fundamental equation for correct steering.

    If this condition is satisfied, there will be no skidding of the wheels when the vehicle takes a turn.

    3. Name approximate straight-line motion mechanisms and explain and prove the point on the link traces exact straight-line path for any one mechanism. (MAY/JUNE 2019[R16])Ans:Approximate straight-line motion mechanisms:

    Watt’s mechanism

    Modified Scott-Russel mechanism

    Grasshopper mechanism

    Tchebicheff’s mechanism

    Robert’s mechanism

    Modified Scott-Russel mechanism

    1) In this mechanism AP is not equal to AQ and points P & Q are constrained to move in the horizontal and vertical directions.

    2) It forms an elliptical trammel, so that any point A on PQ traces an ellipse with semi major axis AQ and semi minor axis AP.

    3) OA = (AP)2 / (AQ).

    4. Explain and prove that the Hart’s mechanism is used for generating exact straight-line motion. (MAY/JUNE 2019[R16])Answer:

    1. It consists of six links i.e., a fixed link OO1 and straight links O1A, FC, CD, DE and EF are connected by turning pairs.

    2. The pin at A is constrained to move along the circumference of a circle.

    3. FC = DE and CD = EF

    4. The points O, A and B divide the links FC, CD and EF in the same ratio.

    From similar triangles CFE and OFB

    (CE/FC) = (OB/OF) ———-(i)

    and from similar triangles FCD and OCA

    (FD/FC) = (OA/OC) ———(ii)

    5. Therefore the product OB X OA remains constant. Hence the point B traces a straight path perpendicular to the diameter OP.

    5. Determine the greatest permissible angle between the axes of the two shafts which are connected by a Hooke’s joint if the maximum variation in the speed of the driven shaft is ± 6 % of the mean speed. The driving shaft is rotating at a uniform speed of 500 rpm. (NOV/DEC 2018[R16])Solution:

    Given Data: N = 500 rpm; ω = 2 π x 500/60 = 52.4 rad/s

    Variation of speed = ± 6 % of the mean speed

    ∴ Total fluctuation of speed of the driven shaft,

    q = 12% of mean speed = 0.12 ω

    6. Show that in Watt’s straight-line motion mechanism, the tracing point P on the coupler divides it in the ratio of the length of the oscillating links which are connected by it. (NOV/DEC 2018[R16])

    1. It is a crossed four bar chain mechanism and in steam engines it guides the piston rod to have an approximate straight-line motion.

    2. In the mean position of the mechanism, links OB and O1A are parallel and the coupling rod AB is perpendicular to O1A and OB.

    3. Arc BB| = Arc AA| or OB x θ = O|Ax Φ   —– (i)

    4. The tracing point P traces an approximate straight line over certain positions of its movement.

    7. Figure (a) shows the Ackermann steering gear in neutral position, and the figure (b) shows the steering gear when the vehicle turns to the right. A table is also given with the values of θ, ϕ, and ϕc where ϕc is the correct value of ϕ required to satisfy the condition for correct steering. Write your inferences from the table. (NOV/DEC 2018[R16])

    स्रोत : rsyamsudhakar.tech

    [Solved] The Ackerman steering gear mechanism is preferred to Davis s

    Explanation: Automobile steering: When a vehicle is making a turn towards one side, the front wheel of that side must swing about the pin through a great

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    The Ackerman steering gear mechanism is preferred to Davis steering mechanism because:

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    Whole of the mechanism in the Ackerman steering gear is the back of the front wheels

    The Ackerman steering gear consists of sliding pairs

    The Ackerman steering gear is most economical

    Davis steering gear consists of turning pairs

    Answer (Detailed Solution Below)

    Option 1 : Whole of the mechanism in the Ackerman steering gear is the back of the front wheels

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    Explanation:

    Automobile steering:

    When a vehicle is making a turn towards one side, the front wheel of that side must swing about the pin through a greater angle than the wheel of the other side.

    The ideal relationship between the swings of the two wheels would be if the axes of the stub-axles, when produced, intersect at a point I on the common axis of the two rear wheels.

    The point I is also the instantaneous centre of the motion of the four wheels.

    Types of Steering gears:

    Davis steering gears.

    Ackermann steering gears.

    Davis Steering Gear

    Ackermann Steering Gear

    It has sliding pairs which mean more friction and easy wearing

    It has only turning pairs and thus less wearing.

    The gear fulfils the fundamental equation of gearing in all positions.

    It drawback is that it fulfils the fundamental equation of correct gearing at the middle and the two extreme positions.

    Ackerman steering gear:

    The Ackerman steering gear mechanism is much simpler than Davis gear.

    The whole mechanism of the Ackerman steering is on the back of the front wheels, whereas in Davis steering gearing, it is on the front of the wheels.

    The Ackerman steering gear consists of turning pairs, whereas Davis steering gear consists of sliding members.

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    स्रोत : testbook.com

    The Ackerman steering gear mechanism is preferred to the Davis steering

    The Ackerman steering gear mechanism is preferred to the Davis steering gear mechanism, because a) Whole of the mechanism in the Ackerman steering gear is on the back of the front wheels b) The Ackerman steering gear consists of turning pairs c) The Ackerman steering gear is most economical d) Both (A) and (B)

    Examveda

    The Ackerman steering gear mechanism is preferred to the Davis steering gear mechanism, because

    A. Whole of the mechanism in the Ackerman steering gear is on the back of the front wheels

    B. The Ackerman steering gear consists of turning pairs

    C. The Ackerman steering gear is most economical

    D. Both (A) and (B)

    Answer: Option D

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