1. AVTC Model Based Design Curriculum Development Project

2. G. Marshall Molen, Ph.D., P.E.
Ergon Distinguished Professor of Electrical and Computer Engineering
Leader of Vehicle Integration at CAVS
Faculty Advisor to the MSU Advanced Vehicle Technology Competition

3. Automotive Transmission
Introduction

4. Introduction to Automotive Transmission
What is a transmission?
An assembly of components that typically make use of gears that alters the speed from the engine to the wheels and the corresponding torque
Floor-mounted shift lever
Splined output shaft
Selector fork shifts gears
Reverse idler gear
Splined input shaft
Synchronizer collar
Countershaft
Source:

5. Basic Concept

6. Powertrain Friction Clutch Fluid Coupling Gear Box
Engine
Transmission
Differential
Friction Clutch
Fluid Coupling
Gear Box
Continuous Variable Transmission
Planetary Gear Set

7. Main Component Gears = x
Rotating components which consists of teeth that mesh with other like components in an assembly that transmits torque
Gear ratio (speed ratio) is the ratio of the angular velocity of input gear to the output gear To ωi Ti ωo x =
Pi = Po
At Gear Interface, V = (ω r)i = (ω r)o
Gear Ratio, iR = ωi/ωo = ro/ri = To/Ti

8. Gear Box Concept

9. Planetary Gear Set

10. Why is it used?
The transmission is commonly used in motor vehicles to transform the engine speed and corresponding torque to the wheels so that the engine is operated in a desired speed range
The engine operates at a high rotational speed relative to the vehicle at slower speeds that include starting and stopping thus the transmission provides more torque at the wheels
Power Available at wheels
In order to overcome the static friction when the vehicle is stationary, it requires high torque to be in motion. After it is in motion, high torque is no longer needed and high speed is required. With the help of transmission we can vary the torque and speed of the vehicle. We can also provide change of direction of the wheels with respect to the engine with the help of the transmission.
Tractive Force
Road Speed, mph
Road Speed, mph
Source:

11. Why is it Used? (cont’d)
When a vehicle is starting from rest the transmission provides higher torque to overcome losses and inertia
Neutral position enables engine to operate without delivering power to the drive wheels
Provides higher torque in low gear and higher speed to driving wheels with higher gear
Provides reverse gear so that the vehicle can move backwards

12. History of Transmission
With the development of the steam engine the necessity arose to adapt the engine power available to intended use. The first steam powered vehicles were driven by a ratchet gear. Higher ratios were required to climb gradients than to drive on a flat surface. In 1784, James Watt patented constant 2-speed gear with a dog clutch engagement. In 1821 Griffith disclosed the 2-speed gearbox with sliding gears, which were extensively used as an inexpensive solution in the early part of the 20th century. After these two major gear configurations were produced, other basic assemblies were developed to provide even better adaptability.

13. Types of Transmissions Used in Automobile Applications
Manual Transmission
Automated Manual Transmission
Automatic Transmission
Continuous Variable Transmission
We will discuss

14. Manual Transmission
A driver operated clutch engages and disengages the power flow from the engine to the transmission using a foot pedal. This temporary interruption in power allows the driver to change the gear ratio by means of a hand operated lever
It allows gears to be shifted when the engine is operating
Source:

15. Automated Manual Transmission
The behavior is similar to a manual transmission except the clutch is operated automatically without input from the driver

16. Automatic Transmission
An automatic transmission shifts automatically through forward gears without use of a lever or clutch
Most automatic transmissions and transaxles have electronic control in addition to hydraulic controls
Typically use a torque converter rather than a clutch
Source:
Fig: Automatic Transmission

17. Continuous Variable Transmission
The relative speed between the input and output shafts is changed by variable diameter pulley that function somewhat similar to a set of gears except that infinite possible ratios can be achieved
Performance is smooth as no abrupt transitions
Engine is operated at optimal speed

18. An Alternate Solution: The Electric Motor
No clutch
Perhaps no gearbox
Constant Torque
Constant Power
Power
Torque
Torque (Nm)
Base Speed
Power (kW)
Speed (rpm)

19. Why Electric Vehicles Don’t Require a Transmission?
Unlike internal combustion engines, electric motors can operate over a wide speed range
There are sophisticated motor drives that provide variable frequencies which enable variations in vehicle speed
Eliminating a transmission from an electric vehicle can significantly reduce the size, weight, and cost of the car

20. Review & Test
What is the main component(s) of an automobile transmission?
Gears
Powertrain
Engine
All the above
When was the first transmission invented?
1987
1977
1784
1894
Which of the following requires a clutch for a vehicle to operate?
Continuously Variable Transmission
Manual Transmission
Automatic Transmission
Automated Manual Transmission
Both b and d

21. References
Chao-Hsu Yao. Automotive Transmissions: Efficiently Transferring Power from Engine to Wheels. ProQuest: Discovery Guides,
G. Lechner, H. Naunheimer and J. Ryborz. Automotive Transmissions: Fundamentals, Selection, Design and Application. Berlin: Springer, 1999.
“Transmission in Automobile,”
“Transmission,”