Exam 20 Marker Structure Flashcards
(9 cards)
HV system components and what they do
High Voltage (HV) is responsible for storing, converting and distributing electrical energy to power vehicle motors and systems
High voltage battery
- Stores electrical energy for propulsion and accessory loads (typically 300-800V)
Inverter
- Converts DC from battery to AC for the traction motor. Also does regenerative braking, converting AC back to DC for charging the battery
Traction motor
- Converts electrical energy into mechanical energy to drive the wheels
Onboard charger
- Converts AC power from the grid (charging stations) into DC to charge the HV battery
DC-DC converter
- Steps down high voltage to low voltage to power conventional systems such as the ECU or lights
Thermal management system
- Maintains optimal operating temperatures for the HV battery, inverter and motor
Battery management system
- Monitors and controls battery temperature, voltage, current and state of charge. Protects battery from overcharging
High voltage safety devices
- HV Contactors are electronically controlled switches that isolate the HV battery, fuses and relays protect circuits from overcurrent and faults and pre charging circuit prevents damage by gradually charging the inverter capacitors
High voltage cables and connectors
- Carry power between components, have orange insulation due to international standard
Hydraulic braking system
How it works
- Driver presses brake pedal and the mechanical force is transferred to the master cylinder
- Master cylinder contains hydraulic brake fluid which produces hydraulic pressure
- Fluid travels through brake lines
- Hydraulic pressure causes the piston in the slave cylinder to move which forces the brake pad / shoe to press against the disc / drum
Pros
- High braking efficiency
- Self lubricating
- Compact and lightweight
Cons
- Fluid leaks lead to failure
- Regular maintenance required
- Not ideal for heavy duty
Disc brakes
How they work
- Driver presses brake pedal and force is transferred through the braking system to calliper at each wheel
- Inside callipers are one or more pistons
- These pistons move inwards, pushing the brakes pads against the brake disc
- This disc is connected directly to the wheel via the hub so it spins with it
- Friction between the pad and the disc slows it down
Pros
- Better heat dissipation
- Easier maintenance
- Lighter than drum brakes
Cons
- Not self servo
- More expensive
- Wear out faster
Drum brakes
How they work
- Brake pedal pressed and force is transferred to callipers through braking system
- Wheel cylinder pushes the piston outwards
- This forces the brake shoe apart
- They press against the inside surface of the spinning brake drum
- The brake drum is attached to the wheel
- As the shoe goes outwards making contact with the drum, friction slows it down and slows the wheel down
Pros
- Self servo
- Lower cost
- Longer life span
Cons
- Poor heat dissipation
- Harder to maintain
- Heavier
Air brakes
How it works
- Air compressor pumps compressed air into storage tanks
- Brake pedal is pressed, foot valve opens which releases air from the reservoirs into the brake chamber
- In each brake chamber there is a diaphragm
- As air enters it pushes the diaphragm which pushes a push rod which forces the brake shoe / pad out
- Releasing the pedal closes the valve and he air is exhausted from the chamber
Pros
- High braking force
- Fail safe design as if fails spring brake engages
- Unlimited air supply
Cons
- Complex
- More maintenance
- Potential air leaks
Fuel cells
How it works and what is it
- Electrochemical device that converts hydrogen and oxygen into electricity, water and heat with no combustion or harmful emissions
- Hydrogen fuel tank stores compressed hydrogen gas
- Hydrogen is sent to the anode side of the fuel cell
- At anode hydrogen is split into electrons and protons
- Electrons go through the external circuit generating electricity
- On cathode side, oxygen from air combines with protons and electrons which results in water as a by product
Components
- Fuel cell tank
- Hydrogen tank
- Air compressor
- Electric motor
- Battery
- Power electronics
Pros
- No emissions
- Quick refuelling
- Long range
-Energy efficient
Cons
- Hydrogen infrastructure
- High cost
- Hydrogen production
- Storage
- Energy loss
Engine materials
Cylinder block, cast iron / aluminium alloy
- Cast iron strong wear resistant and cheap
- Aluminium alloy is light and conducts heat well
Cylinder head, aluminium alloy
- Handles heat well, light weight and easy to machine
Pistons, aluminium alloy
- Lightweight, reducing mass allowing for better acceleration and efficiency and good thermal conductivity, can withstand high pressures and temperatures
Piston rings, steel
- Hard, wear resistant to maintain good seal
Connecting rods, forged steel /titanium
- Strong and can handle high compressive and tensile forces
Crankshaft, forged steel / cast iron
- Must withstand high rotational forces and torque, forged steel offers excellent strength and fatigue résistance
Valves, heat resistive steels
- Exhaust valves operate it hot conditions and must resist corrosion and temperatures
Camshaft, cast iron / forged steel
- Strong and wear resistant
Servo assistance
- When you press brake pedal, a rod moves in the servo unit
- This contains a diaphragm and uses an engine vacuum on one side
- As you apply the brake, atmospheric pressure is allowed into one side of the diaphragm
- The pressure difference across the diaphragm creates extra force which helps push the master cylinder
Can be done hydraulically using pressure from power steering or using electric motors
Sprung and unsprung mass
Sprung mass
- The mass supported by the suspension, can be thought of as everything above the suspension rings
Un sprung mass
- The mass not supported by the suspension, parts that move with the wheels, below suspension rings
Pros of lower un sprung mass
- Better ride quality as less shock is transferred to vehicle body
- Improved handling as reduces interia of parts in contact with the road
