Deck 41: Electric Powertrains

Question 1

When a regenerative braking cycle is engaged in a vehicle with an electric powertrain, which of the following should be true?

A) The driveshaft turns in reverse.
B) The ICE compression retarder is actuated.
C) The traction motor generates AC.
D) The traction motor generates DC.

Answer 1

The traction motor generates AC.

Question 2

Which of the following best describes the category of batteries that tends to be used in most current commercial electric vehicle powertrains?

A) Alkaline
B) Lead acid
C) Lithium-ion (Li-on)
D) Nickel cadmium (Ni-cad)

Answer 2

Lithium-ion (Li-on)

Question 3

Which of the following is true of the traction motor/generator used in a CEV?

A) It generates multi-phase AC power.
B) It requires the use of an inverter.
C) Output must be rectified to DC to be stored battery banks.
D) All of the above.

Answer 3

All of the above.

Question 4

Technician A says that UCs can store large amounts of electrical energy but discharge it more slowly than most types of batteries. Technician B says that some UCs will sustain up to a million charge and discharge cycles. Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 5

Which of the following cities was the first to eliminate diesel engines from its transit bus fleet?

A) Chicago
B) Houston
C) Los Angeles
D) New York City

Question 6

When a li-ion battery is charged, which of the following is true?

A) lithium ions move from the cathode to the anode
B) lithium ions move from the anode to the cathode
C) lithium ions are discharged into the ground circuit
D) a thermal runaway is likely

Question 7

While a li-ion battery is being discharged, which of the following is true?

A) lithium ions move from the cathode to the anode
B) lithium ions move from the anode to the cathode
C) lithium ions are discharged into the ground circuit
D) a thermal runaway is likely

Question 8

Technician A says that although the voltage is high in a CEV, there is usually insufficient available current to cause an injury. Technician B says that the RESS in a CEV can output HV exceeding 600 volts. Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 9

Where would you most likely find a pantograph on a CEV transit bus?

A) In the forward engine compartment
B) In the rear engine compartment
C) Below the floor deck
D) On the roof

Question 10

Which of the following methods of charging a CEV from the grid is contact-free?

A) Inductive
B) Overhead pantograph
C) Stationary pantograph
D) CCS type 2 coupler

Question 11

Technician A says that a CEV pantograph can be a permanent station fixture. Technician B says that a CEV stationary pantograph can uses a flexible parallelogram to enable its contact rails to connect with contactors on the vehicle. Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 12

Technician A says that the peak torque ratings for CEV traction motors exceeds that used in an equivalent ICE by a significant margin. Technician B says that CEV traction motors typically have higher power ratings than the ICEs used in an equivalent vehicle. Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 13

Which of the following correctly describes a typical CEV traction motor?

A) Series-wound 600 volt DC motor
B) Series-wound 24 volt DC motor
C) Synchronous 24 volt single phase AC motor
D) Synchronous 600 volt 3-phase AC motor

Question 14

Where is a CEV string control unit (SCU) normally located?

A) Engine ECM
B) Inverter module
C) Battery disconnect unit (BDU)
D) Chassis management module

Question 15

What is the function of a typical battery disconnect unit (BDU)?

A) power distribution
B) communications with chassis data bus
C) current sensing
D) all of the above

Question 16

What device performs the high speed switching required in a solid state inverter?

A) FET
B) IGBT
C) Diode
D) Electromechanical rotary wheel

Question 17

What frequency AC is used on the North American grid?

A) 600 hertz
B) 120 hertz
C) 60 hertz
D) 24 hertz

Question 18

Which of the following li-ion cells has proven to be the most thermally stable?

A) LFP
B) NCA
C) LTO
D) NMC

Question 19

How many NMC cells are required to produce a pack voltage of over 80 VDC?

A) 1
B) 8
C) 12
D) 22

Question 20

Technician A says that li-ion packs are arranged in parallel to form a string. Technician B says that battery strings are arranged in series to form a bank. Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 21

How many NMC strings would have to be placed in series to produce a bank voltage that exceeds 600 VDC?

A) Seven
B) Five
C) Four
D) Three

Question 22

Technician A says that using multiple battery banks in parallel increases the electrical energy density. Technician B says that CEVs use multiple battery banks in series to increase the nominal operating voltage. Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 23

Which of the following best describes the source of the energy recovered during regenerative braking in an electric powertrain?

A) Battery banks
B) Inverter module
C) Traction motor
D) Vehicle momentum (kinetic energy)

Question 24

Technician A says that that some CEVs are driven by a single, longitudinally-mounted (inline) traction motor directly coupled to drive wheels. Technician B says that a CEV drive axle can use a pair of in-axle traction motors coupled to reduction gearing in each wheel assembly. Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 25

Technician A says that some CEVs use 6-phase AC traction motors. Technician B says that some CEVs use 9-phase AC traction motors Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 26

What would be the advantage of using a 9-phase traction motor over a 3-phase motor in a CEV?

A) Lower cable operating temperatures
B) Use of lower sectional area wiring
C) Increased power
D) All of the above