Question

Q12. Overdrive is provided in the transmission of
a vehicle to
(A) improve fuel consumption
(B) reach higher road speeds
(C) achieve better acceleration
(D) None of the above​

Answer 1

Overdrive is the operation of an automobile cruising at sustained speed with reduced engine revolutions per minute (RPM), leading to better fuel consumption, lower noise, and lower wear.[1] Use of the term is confused, as it is applied to several different, but related, meanings.[1]

The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is over-geared, and cannot reach its potential top speed, i.e. the car could travel faster if it were in a lower gear, with the engine turning at higher RPM.[1]

1960s Triumph gearbox with Laycock de Normanville electro-hydraulic operated overdrive

Laycock de Normanville "J type" overdrive unit

The purpose of such a gear may not be immediately obvious. The power produced by an engine increases with the engine's RPM to a maximum, then falls away. The point of maximum power is somewhat lower than the absolute maximum RPM to which the engine is limited, the "redline" RPM. A car's speed is limited by the power required to drive it against air resistance, which increases with speed. At the maximum possible speed, the engine is running at its point of maximum power, or power peak, and the car is traveling at the speed where air resistance equals that maximum power. There is therefore one specific gear ratio at which the car can achieve its maximum speed: the one that matches that engine speed with that travel speed.[1] At travel speeds below this maximum, there is a range of gear ratios that can match engine power to air resistance, and the most fuel efficient is the one that results in the lowest engine speed. Therefore, a car needs one gearing to reach maximum speed but another to reach maximum fuel efficiency at a lower speed.

I hope you are understand my solution

Answer 2

Overdrive is provided in the transmission of a vehicle to (A) improve fuel consumption.

What is the purpose of overdrive?

• Overdrive prevents maximum power and acceleration when a vehicle generally operates at lower ratios with more output and torque.
• The car is said to be "over-geared" or "overdriven," sacrificing peak speed and performance for better fuel efficiency and a more comfortable ride.
• OD often raises shift points to higher RPMs.
• Leave OD off if you want to accelerate quickly.
• Leave it on for better fuel efficiency and a calmer ride.
• An overdrive gear can save engine wear and increase fuel efficiency, but only when employed in situations where there is little torque demand.
• Since the link between the engine and the drive wheels that multiplies torque while a gearbox is in overdrive is inverted, overdrive in conjunction with a high torque demand is problematic.

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