Question 1

When electricity is used to directly power traction motors, what is the highest rate of thermal efficiency in current vehicles?

Accepted Answer

The answer of When electricity is used to directly power...

Question 2

Which of the following is required for a hydrogen fuel cell to produce electricity?

Accepted Answer

Hydrogen fuel cells produce electricity through a chemical reaction between hydrogen (fuel) and oxygen from the air.

Question 3

What results from the electrochemical reaction in a hydrogen fuel cell?

Accepted Answer

In a hydrogen fuel cell, hydrogen and oxygen react in an electrochemical process to produce electricity and water as by-products.

Question 4

Which type of fuel cell is currently favored by commercial vehicles?

Accepted Answer

Proton exchange membrane (PEM) fuel cells are favored by commercial vehicles due to their low operating temperature, quick start-up time, and suitability for applications requiring varying power outputs, such as vehicles.

Question 5

Technician A states that an advantage of a parallel hydraulic hybrid (PHH) drive system is that a small bore ICE can be used in place of a larger one. Technician B states that a PHH system can only impart hydraulic drive torque, so that in the event of a leak, the vehicle would be crippled. Who is correct?

Accepted Answer

Technician A is correct because a parallel hydraulic hybrid system allows for a smaller internal combustion engine (ICE) to be used by supplementing the engine's power with hydraulic power, thus reducing the need for a larger engine. Technician B is incorrect because a PHH system can provide both hydraulic and mechanical drive torque, meaning the vehicle can still operate even if there's a hydraulic leak, though perhaps with reduced efficiency.

Question 6

When a blended torque transmission is used in an HEV drivetrain transit bus, which of the following features are possible?

Accepted Answer

A blended torque transmission in an HEV drivetrain allows for input torque from multiple sources (such as an internal combustion engine and an electric motor), continuously variable output ratios, and infinitely variable output speeds, making all the listed features possible.

Question 7

What type of hydraulic accumulator is used in Eaton PHH and SHH drive systems?

Accepted Answer

Eaton PHH and SHH drive systems use nitrogen gas-loaded accumulators at 5,000 psi (345 bar) to store hydraulic energy. This type of accumulator is efficient for energy storage and release, making it suitable for these drive systems.

Question 8

Technician A says that HEV buses can use NG-fueled engines. Technician B says that HEV buses can use diesel engines. Who is correct?

Accepted Answer

Hybrid Electric Vehicles (HEVs) can be designed to use various types of internal combustion engines, including both natural gas (NG) and diesel engines, to complement the electric drive component. This flexibility allows for a range of fuel options depending on availability, cost, and environmental considerations.

Question 9

Which of the following is true of an HEV powertrain used in a typical urban vehicle?

Accepted Answer

Hybrid Electric Vehicles (HEVs) have powertrains that can generate drive torque through both electrical and mechanical means, depending on the driving conditions and the state of charge of the battery. This allows for efficient operation by utilizing the electric motor, the internal combustion engine, or both.

Question 10

Which of the following accounts for the significantly lower emissions produced by the small bore ICE used in an HEV?

Accepted Answer

All the options contribute to the significantly lower emissions produced by the small bore Internal Combustion Engine (ICE) used in a Hybrid Electric Vehicle (HEV). Running the ICE at its optimum speed ensures maximum efficiency, using less fuel directly reduces emissions, and the specific mention of a substance (though fictional) implies a reduction in harmful emissions.

Question 11

When a hydrogen fuel cell cogenerates waste heat, what happens to its overall thermal efficiency?

Accepted Answer

When a hydrogen fuel cell cogenerates waste heat, its overall thermal efficiency can rise to 80% because the waste heat is utilized for heating or other purposes, thereby increasing the efficiency of energy use.

Question 12

In a hydrogen fuel cell commercial vehicle, where is the DC electricity stored?

Accepted Answer

RESS (Rechargeable Energy Storage System), typically a battery or supercapacitor, stores DC electricity in a hydrogen fuel cell vehicle. The fuel cell generates electricity through a chemical reaction between hydrogen and oxygen, and this electricity is then stored in the RESS for use by the vehicle's electric motor and other electrical systems.

Question 13

In an HEV equipped with a blended torque transmission (BTT), what is usually providing torque to the wheels at vehicle launch?

Accepted Answer

In a Hybrid Electric Vehicle (HEV) equipped with a blended torque transmission (BTT), the BTT motor usually provides torque to the wheels at vehicle launch. This is because electric motors can deliver maximum torque from a standstill, which is ideal for smooth and efficient launches.

Question 14

Technician A says that a series hydraulic hybrid (SHH) drive options either direct mechanical or full hydraulic motor drive. Technician B says that the Eaton HLA is a parallel hydraulic hybrid (PHH) system. Who is correct?

Accepted Answer

Technician B is correct because the Eaton Hydraulic Launch Assist (HLA) system is indeed a parallel hydraulic hybrid (PHH) system, which means it works alongside the conventional powertrain to provide additional power. Technician A's statement is incorrect because a series hydraulic hybrid system does not offer a direct mechanical drive option; it operates by converting mechanical energy into hydraulic energy and then back into mechanical energy to drive the wheels.

Question 15

Technician A says that the HLA accumulator can be loaded with hydraulic pressures up to 5,000 psi. Technician B says that the Eaton HLA drivetrain uses a reversible hydraulic piston pump/motor. Who is correct?

Accepted Answer

Technician B is correct because the Eaton HLA (Hydraulic Launch Assist) system indeed uses a reversible hydraulic piston pump/motor to store energy and assist in vehicle propulsion. Technician A's statement about the HLA accumulator being loaded with pressures up to 5,000 psi is incorrect; typical systems operate at lower pressures.

Question 16

Which of the following is true of regenerative braking in an HEV commercial vehicle?

Accepted Answer

Regenerative braking in a Hybrid Electric Vehicle (HEV) involves converting the kinetic energy during braking into electrical energy. This process typically involves converting the mechanical energy into AC (alternating current) first, then converting this AC into DC (direct current), and finally storing this DC in the vehicle's Rechargeable Energy Storage System (RESS). Thus, all the steps mentioned are part of the regenerative braking process.

Question 17

When is the ICE most likely to be required to mechanically power a HEV drivetrain?

Accepted Answer

The answer of When is the ICE most likely to...

Question 18

Which of the following powertrains does not use an internal combustion engine (ICE)?

Accepted Answer

PEM fuel cell drivetrains do not use an internal combustion engine. Instead, they generate electricity through a chemical process in a fuel cell, typically using hydrogen as fuel, to power an electric motor.

Question 19

Where are the hydrogen cylinders usually located on a fuel cell powered transit bus?

Accepted Answer

Hydrogen cylinders on a fuel cell powered transit bus are usually located on the roof to save space, ensure safety, and facilitate the dissipation of any potentially leaked hydrogen into the atmosphere.

Question 20

What effect does cryo-compression have on the hydrogen that is used to power fuel cells?

Accepted Answer

Cryo-compression increases the density of hydrogen by cooling it to very low temperatures and compressing it, which allows for more efficient storage and transport for use in fuel cells. It does not reduce its weight or make it less flammable.

Quiz 40: Hybrid and Hydrogen Fuel Cell Drivetrains