# Vehicle Dynamics MCQ – Set 5

This set of Vehicle Dynamics Multiple Choice Questions & Answers (MCQs) focuses on “Automatic Transmission and Gear Ratios in Acceleration Performance”.

1. What component transmits power from the engine to the gear train in an automatic transmission?
a) torque converter
b) clutch
c) gear
d) shaft

Explanation: Torque converters are fluid couplings that amplify torque input to transmission from the engine using hydrodynamic principles. Torque transmission occurs at the expense of speed. Clutch is used in the manual transmission to transmit power from the engine to the transmission.

2. Automatic transmissions have a _____ output to input torque ratio at zero output speed when compared to manual transmissions
a) equal
b) lower
c) higher
d) negligible

Explanation: At zero output speed, the output torque would be several times the input torque. It is almost twice the engine torque when the transmission is stalled. This provides a good off-the-line acceleration of an automatic vehicle.

3. What is the torque ratio (output/input) when the transmission output reaches engine speed in an automatic transmission?
a) 2:1
b) 1:1
c) 1:2
d) 1:5

Explanation: As speed builds up in an automatic transmission, the torque ratio gradually drops from the maximum. The torque ratio is almost unity when the transmission speed is equal to the engine speed. It is almost twice the engine torque when the transmission is stalled. During overdrive conditions, the torque ratio may drop below unity.

4. Torque curves in each gear can extend down to zero speed without stalling the engine in an automatic transmission.
a) True
b) False

Explanation: The torque converter in the automatic transmission is a fluid coupling. This fluid coupling can allow slip. Thus, torque curves in each gear can extend down to zero speed without stalling the engine.

5. Maximum fuel economy is achieved in the lower gears.
a) True
b) False

Explanation: Maximum fuel economy is achieved in the cruising range which occurs in the higher gears. The first gear is used for starting, second and third gear is usually used for passing and a hih=gh gear is normally suited for fuel economy at road speeds.

6. Which relationship governs the gear ratios used in production cars?
a) harmonic progression
b) arithmetic progression
c) random progression
d) geometric progression

Explanation: Although the gear ratios in production cars are normally close to a geometric progression, there can be variations. This ratio is decided by the design engineers during transmission or gearbox design. Design ratios are commonly obtained from the series such as R-10 and R-20.

7. With increasing output to input speed ratio of an automatic transmission, the efficiency _____
a) increases
b) decreases
c) remains the same
d) oscillates

Explanation: The efficiency of the automatic transmission increases from zero, which is when the transmission is stalled. It increases as the speed of the transmission increases and almost reaches an asymptote at the higher output to input speed ratios.

8. Which of the following is not a part of the planetary gear set used in automatic transmissions?
a) sun gear
b) planet gear
c) ring gear
d) dog clutch

Explanation: Dog clutch is a part of the manual transmission. It is used to engage and disengage the various gears in a manual transmission. The sun, planet and the ring gear from an epicyclic gear set in an automatic transmission. A combination of such gear sets gives the various gear ratios.

9. What does the intersection of the road load curves and the tractive efforts curves indicate?
a) maximum speed that can be sustained in that gear
b) minimum speed that can be sustained in that gear
c) maximum acceleration that can be sustained in that gear
d) minimum acceleration that can be sustained in that gear

Explanation: Intersection of the road load curves and the tractive efforts curves indicates the maximum speed that can be sustained in that gear. A constant speed is reached when all of the engine power is used to overcome the road loads and internal losses, at a particular gear. Thus, acceleration would be zero.

10. Passenger cars transmission design should aim to maximize_____
a) power
b) fuel economy
c) top speed
d) fuel consumption

Explanation: Transmission should be designed such that the best fuel economy is maintained throughout the driving range of passenger cars. Power and top speed maximization is usually the requirement in motorsports.

Sanfoundry Global Education & Learning Series – Vehicle Dynamics.

To practice all areas of Vehicle Dynamics, here is complete set of Multiple Choice Questions and Answers.

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