Module 8 Practice

Question 1

List and describe the functionality of the components of a typical SM1ST drivetrain. How does this design differ from a typical ICE FWD drivetrain?

Answer 1

• Electric Motor
• Transmission: Modifies the relationship between speed and torque to keep engine in power band. Also provides forward, reverse, etc
• Differential: Allows two wheels to be driven from the same input, at different speeds (for turning w/o dragging one wheel). Limited slip variants avoid power dumping.
• Wheels

Main difference: no clutch/torque converter

Question 2

What is the difference b/w AWD and 4WD?

Answer 2

• AWD sends power to either the front or rear axle in normal driving conditions. If the vehicle detects a lack of traction, it will engage all wheels. Needs to have controllable mechanism at each wheel needs tocbe some mechanism to vary the power at each wheel.
• 4WD has a selectable switch to choose 2WD mode or 4WD mode depending on road conditions –> more control over where power goes.

Question 3

Why is reduction gearing and differential gearing needed in an EV? Are there any variants of the EV that change the need for gearing? How can a CVT improve EV operation?

Answer 3

• most motor types run at elevated speeds (base-NL), even compared to ICE upper-end. Reduction gearing is still needed. Minimum viable: Planetary at each motor or implement in the differential. Best option is active transmission or CVT.
• Single Motor, 2-Speed Transmission requires gearing
• CVT (Continuous Variable Transmission): provides a smoothly-varying speed ratio without the use of distinct gear pairs
• belt/chain drive (pulley connects from input-output)
• smoothly varying the radius of the pulleys that the belt is riding on, by moving the plates further or closer together, we can created a continuously changing ratio, in response to a changing load.
• CVT improves EVs by allowing for
• efficient power delivery bc the motor will always be operating at the ideal RPM for the load demand
• Extended Battery Life: Because a CVT minimizes sudden torque demands, it reduces peak loads on the motor and battery, potentially extending the lifespan of these components.
• smoother accelleration

Question 4

Describe the operating principles behind the two main dual motor EV drivetrain variants (DMPAT, DMPGT). What is the design intent behind each pattern?

Answer 4

Dual Motor Parallel Axle Transmission (DMPAT)
- second motor enables AWD-like implementation
-2 EMs at front and rear, single speed transmission, differential, axles and wheels

Dual Motor Planetary Gear Transmission (DMPGT)
- improve key driving metrics (accelleration , coasting, efficiency, range)
- second motor can operate with a different target OP (one motor low speed/high torque, one motor high speed/low torque)
- front wheel drive
- front axle w/ differential, dual motor set up (coupled to drive the same set of wheels), apply ratio b/w motors to select different motor types to work individually or in tandem to expand range of operating points - motor modes
- motors connected by inverter and then to battery

Question 5

Explain the concept of torque vectoring as it applies to EVs

Answer 5

• per wheel torque modification
• reducing under/oversteer, improving handing and responsiveness, traction control
• allow driver to better adapt to direction the car is going and varying road conditions
• computer system senses the indented steering direction to adjust torque at each wheel.
• mechanically leaning concept: after the differential, add split axle w/ planetary gear train after the differential to the driven wheels that shifts amounts of torque to the wheels
  -Electrically-leaning concept: adjust drive output per-
  wheel, possibly in combination with/via other systems.

Question 6

Explain the concept of torque blending and how it interacts with regenerative braking.

Answer 6

• driver steps on brake and EM switches to generator mode.
• wheels transfer kintetic energy tothe motor/generator via the drivetrain
• geerator converts kinetic energy to electrical energy and stores it in the battery
• generative braking torque decelleratest the vehicle
• at low speeds, the generator can not longer supply sufficient generation torque to stop the vehicle and the braking torque from the friction brake is adapted tothe current generative braking torque to stop the car.

Question 7

Explain the concept of one-pedal driving, including its benefits and limitations.

Answer 7

• Requires complex control schema; understanding of
  vehicle dynamics, haptics implementation,
  prediction of driver intent.
• In theory a superior method – reduces pedal
  transitions greatly. Contentious in practice; no
  coasting method.