Lesson 16: Vehicle Technology PDF

Lesson 16: Vehicle Technology Overview The automotive industry is in the midst of an amazing revolution. This revolution is not only shaping up to be highly disruptive to the traditional transportation industry, but is also relatively unique among the transitions going on in the world's current ene...

Lesson 16: Vehicle Technology Overview The automotive industry is in the midst of an amazing revolution. This revolution is not only shaping up to be highly disruptive to the traditional transportation industry, but is also relatively unique among the transitions going on in the world's current energy system in that the revolution is largely being driven by consumer demand rather than by government regulations. At the heart of this revolution are breakthrough innovations in three main areas: (1) power trains or the components that power vehicles, (2) drivetrains or the components that translate that power to the wheels of vehicles, and (3) the use artificial intelligence designed to initially improve the safety of, but now increasingly takeover many driving tasks. Given the limited amount of material that we can cover in this class, this lesson foregoes discussing the more recent advances in incorporating AI in vehicle operations, and instead focuses down on the two changes that are ushering in the electrification of transportation; electric power and drive trains. And to fully appreciate the benefits of these changes, the lesson begins by first reviewing how the power and drive trains of conventional vehicles work. These were and remain remarkable innovations in their own right, and for now still remain the dominant means by which vehicles operate. Lecture Outline 1. There are three basic ways to reduce CO2 emissions from transportation: a. Find a lower CO2-emitting fuel that can readily be substituted for gasoline, diesel and jet fuel b. Increase transportation efficiency, and/or c. Shift to a different form of energy for transportation. 2. This lesson focuses on options (2) and (3) both of which are part of the transportation sector’s shift towards electric engines and drivetrains a. Drivetrains = mechanics of how engine motion drives wheel motion 3. To understand the significance of this shift requires first understanding how an internal combustion engine and standard drive train works 4. How an internal combustion engine (ICE) works a. Everything in the ICE is interlinked i. Down-up strokes of the pistons in the engine cylinders rotate the crankshaft ii. Crankshaft turns a timing belt iii. Timing belt rotates the camshafts iv. Camshafts open and close fuel and exhaust valves to each cylinder.\ b. Strokes in a four-stroke engine are: i. Down for intake ii. Up for compression iii. Down in response to fuel-air combustion iv. Up for exhaust c. Combustion is triggered by a spark plug, which fires at the top of the compression upstroke d. Rotating crankshaft also… i. Turns a flywheel at the back of the engine, the rotation of which gets translated by the drivetrain to the vehicle’s wheels ii. Powers the car’s electric generator. e. The generator keeps the battery charged f. The battery ends electricity to the distributor. g. The distributor has a rotating contact, which sends electricity to the proper spark plug at the proper time so that it fires off just as the piston in the cylinder reaches the top of its compression stroke. h. And the spark timing is tied to the rotation of the camshaft that opens the cylinder valves to release the combusted gas emissions immediately after the bottom of the combustion stroke 5. The Difference between a Gasoline and Diesel Engine  a. Gasoline readily evaporates and thus mixes with air, and it can be ignited with a spark i. This is why ICEs use spark plugs b. Diesel does not readily evaporate in air, but if injected into air as an atomized mist and then heated to a high enough temperature, the diesel-air mixture will spontaneously combust i. A high enough temperature is achieved by sufficient pressure during the compression stroke 1. From the ideal gas law, in which temperature is directly proportional to pressure ii. Consequently, diesel engines have fuel injectors rather than spark plugs c. This is part of the reason why diesel engines are more efficient than ICEs; the fuel can be compressed more than gasoline before combusting, allowing for a longer piston stroke and thus more power output 6. How a Conventional Vehicle Drivetrain Works a. The engine fly wheel is connected to the drive shaft via a countershaft and a clutch shaft, across which different sized gears are moved and enmeshed with one another. b. When a small gear being turned by the countershaft turns a larger gear that spins the drive shaft, the drive shaft turns slower than the engine shaft, but has more torque. c. To make the drive shaft turn faster, the gear on the counter shaft must progressively be switched to enmeshing with a smaller and smaller gear on the drive shaft. d. As you accelerate your car, the RPMs of the engine flywheel will increase up to a point before the transmission shifts the car into a higher gear, at which point the engine RPMs will fall and then begin to rise again as you accelerate further. e. Note that gears allow for different wheel speeds and even spin directions from speed that the engine is turning. f. The differential at the end of the drive shaft…  i. Rotates the drive shaft’s spin direction 90° ii. Allows the wheels to rotate at different speeds when turning. 1. If wheels couldn’t spin at different speeds during a turn, the axel would bend. 7. How an Electric Motor Works a. An electric induction motor has the same two main parts: a fixed stator that surrounds a rotor that can spin i. Just like an electric generator b. The stator is electrified with three phase current, each phase being 120° displaced from the other two c. The cycling of the AC current in each phase creates a rotating magnetic field around the rotor, which containing conductive material, becomes electrified with its own AC current d. The AC current in the rotor generates a magnetic field that is in opposition to the stator’s rotating magnetic field, and so is pulled by the latter, turning the rotor. e. If the rotor succeeds in spinning at the same speed as the stator’s rotating magnetic field, it no longer experiences a fluctuating magnetic field and becomes de-electrified, killing off its own magnetic field and with it the magnetic pull being produced by the three-phase current in the stator. f. In this case, the spinning rotor slows and falls out of sync with the rotating magnetic field produced by the stator and once again becomes electrified and pulled to rotate. g. The roles can be flipped of the stator and rotor can be flipped, i.e. the rotor can be turned to produce three-phase AC current that comes out of the stator i. The motor then becomes a generator ii. The outgoing electricity is used to charge the batteries 8. How a Hybrid Electric Vehicle Works a. There have been three powertrain configurations for HEV’s  i. Parallel configuration, in which the electric motor is connected to the internal combustion engine and helps the latter turn the wheels. ii. Series connection, in which the electric motor is the only motor that turns the wheels, and the internal combustion engine is only used to drive a generator that keeps the battery powering the electric motor charged iii. And power-split configuration, which uses a combination of the other two configurations b. Hybrids can also be classified in terms of their electric power output i. Mild hybrids are those with a parallel powertrain configuration 1. The electric motor assists the internal combustion engine during acceleration and then becomes a generator during breaking, storing the recovered energy in the same second battery that the electric engine draws upon during acceleration ii. Full hybrids use the power-split powertrain configuration 1. They can be powered by the electric engine, the internal combustion engine, or both together, with the best option being determined by a microcomputer in the car programmed to maximize fuel efficiency iii. Plug-in hybrids are similar to full hybrids, but have a much larger second battery, allowing them to be driven for longer distances on the electric motor alone 1. These have the highest fuel efficiency. 9. How a Pure Electric Vehicle Works a. Motor speed is changed by changing the frequency of the three-phase current in the stator i. The higher the frequency, the faster the motor turns, and vice versa. b. An electric motor can achieve significantly higher RPMs than an internal combustion engine i. The latter requires a transmission with multiple gears to translate its limited RPM range into faster speeds  ii. The higher RPM range of an electric motor on the other hand allows it to turn the wheels at these higher speeds on its own and thus with only a single-gear transmission c. Furthermore, whereas a number of moving parts are required to achieve a smooth output from linear motion of the pistons in an internal combustion engine, an electric induction engine produces smooth output on its own, and it is self-starting and so does not need spark plugs to get the engine going d. The electric motor in a pure electric vehicle is coupled to an inverter, which converts DC current from the car’s battery pack to the three-phase AC current needed to run the electric motor e. The inverter also controls the frequency and amplitude of the AC current, thereby managing the speed and power output of the electric motor f. The battery pack in the Tesla is made up of thousands of lithium ion batteries which are somewhat bigger than a standard AA battery i. The batteries are arranged so as to provide significant energy storage and power output and are kept from overheating by a coolant that passes around the battery through a winding innertube g. Control of the power supply to the wheels allows them to be spun at different speeds and thus provide all-wheel drive h. The Tesla is a much simpler car than a conventional car in that it has far fewer moving parts 10. Other Ongoing Changes in the Transportation Sector a. App-based ride and car services i. Uber, Lyft ii. Zipcar b. Impact of Covid on increasing work from home