CPC Vehicle Systems — Questions and Answers
Question 1: What is the function of the turbocharger in a modern HGV diesel engine?
- To reduce exhaust noise
- To force more air into the engine cylinders, increasing power output and efficiency (Correct answer)
- To cool the engine
- To filter fuel before injection
Correct answer: To force more air into the engine cylinders, increasing power output and efficiency
A turbocharger uses exhaust gas energy to spin a turbine that compresses intake air, forcing more air (and therefore more fuel) into the combustion chambers. This increases power output without increasing engine size, also improving fuel efficiency.
Question 2: What is the purpose of the EGR (Exhaust Gas Recirculation) system?
- To increase engine power
- To reduce nitrogen oxide (NOx) emissions by recirculating a portion of exhaust gas back into the engine (Correct answer)
- To improve fuel economy by reusing fuel
- To reduce exhaust noise levels
Correct answer: To reduce nitrogen oxide (NOx) emissions by recirculating a portion of exhaust gas back into the engine
The EGR system reduces NOx emissions by recirculating a controlled amount of exhaust gas back into the intake manifold. This lowers combustion temperatures, which reduces the formation of nitrogen oxides, a major pollutant.
Question 3: What type of braking system do most modern HGVs use?
- Cable-operated brakes
- Air-operated (pneumatic) disc or drum brakes (Correct answer)
- Hydraulic brakes only
- Electric brakes only
Correct answer: Air-operated (pneumatic) disc or drum brakes
Most modern HGVs use air-operated (pneumatic) braking systems with disc or drum brakes. Compressed air operates the brake chambers, which push the brake pads against the disc or drums against the shoes. Air brakes are preferred because they are fail-safe.
Question 4: What is the function of the air compressor in an HGV?
- To inflate tyres while driving
- To generate compressed air for the braking system, suspension, and other pneumatic systems (Correct answer)
- To power the air conditioning only
- To clean the engine air filter
Correct answer: To generate compressed air for the braking system, suspension, and other pneumatic systems
The engine-driven air compressor generates compressed air that is stored in air tanks and used to operate the brakes, air suspension, and other pneumatic systems. Maintaining correct air pressure is critical for brake safety.
Question 5: What does the ABS (Anti-lock Braking System) do on an HGV?
- It stops the vehicle faster in all conditions
- It prevents the wheels from locking during heavy braking, allowing the driver to maintain steering control (Correct answer)
- It automatically applies the brakes when an obstacle is detected
- It reduces brake wear during normal driving
Correct answer: It prevents the wheels from locking during heavy braking, allowing the driver to maintain steering control
ABS prevents wheel lock-up during heavy braking by rapidly modulating brake pressure to individual wheels. This maintains tyre grip and allows the driver to continue steering the vehicle while braking, reducing the risk of jackknifing and skidding.
Question 6: What is the purpose of the differential in an HGV drivetrain?
- To change the engine's fuel supply
- To allow the driven wheels to rotate at different speeds when cornering (Correct answer)
- To provide additional braking force
- To connect the trailer to the tractor unit
Correct answer: To allow the driven wheels to rotate at different speeds when cornering
The differential allows the driven wheels on the same axle to rotate at different speeds during cornering. The outer wheel travels a greater distance than the inner wheel, so must rotate faster. Without a differential, the tyres would scrub and handling would be dangerous.
CPC Vehicle Systems
What is the function of the turbocharger in a modern HGV diesel engine?