CHAPTER IV
DRIVELINE DYNAMICS
I.
II.
III.
IV.
ENGINE DYNAMICS
DRIVELINE AND EFFICIENCIES
GEAR BOX AND CLUTCH DYNAMICS
GEAR BOX RATIO
I. ENGINE DYNAMICS
For indirect injection For direct injection
Diesel engines
Diesel engines
A sample of power and torque
performances for a spark ignition engine
I. ENGINE DYNAMICS
An example of power performance in a spark ignition engine with constant
efficiency contours
II. DRIVELINE AND EFFICIENCIES
2.1 Driveline
Driveline components of a rear wheel drive vehicle
II. DRIVELINE AND EFFICIENCIES
2.1 Driveline
The input and output torque and angular velocity of each driveline component
III. GEAR BOX AND CLUTCH DYNAMICS
3.1 Velocity and Traction Force
III. GEAR BOX AND CLUTCH DYNAMICS
3.2 Velocity and Traction Force - example
III. GEAR BOX AND CLUTCH DYNAMICS
3.2 Velocity and Traction Force - example
A sample of a gear-speed plot for a gearbox
III. GEAR BOX AND CLUTCH DYNAMICS
3.2 Velocity and Traction Force - example
Wheel torque-speed at each gear ni of a gearbox
III. GEAR BOX AND CLUTCH DYNAMICS
3.3 Acceleration capacity at different speed
An example for the acceleration capacity ax as a function of forward speed vx
III. GEAR BOX AND CLUTCH DYNAMICS
3.4 Gear box stability condition
When we shift the gear to ni−1 the engine speed ωe jumps to a higher speed
ωe = ωi−1 >ωT at the same vehicle speed
The stability condition requires:
A simple rule for a stable gearbox design
III. GEAR BOX AND CLUTCH DYNAMICS
3.5 Example - Gear box stability condition
Transmission ratios and stability condition
The stability condition requires that ni−1/ni = cte
III. GEAR BOX AND CLUTCH DYNAMICS
3.5 Example - Gear box stability condition
Using n1 and n6
IV. GEAR BOX RATIO
used to calculate the gear ratios of a
gearbox as well as vehicle performance
- Engine should work at its maximum power to have the best performance.
- To control the speed of the vehicle, we need to vary the engine’s angular velocity.
- The engine’s working range: (ω1,ω2) around ωM, which is associated to the
maximum power PM.
Recommendations to design the transmission ratios of a vehicle gearbox
1.Design the differential transmission ratio nd and the final gear nn such that the
final gear nn is a direct gear, nn=1, when the vehicle is moving at the
moderate highway speed.
2.Same as item 1, however, when the vehicle is moving at the maximum
attainable speed.
3.The first gear n1 may be designed by the maximum desired torque at driving
wheels, (determined by the slope of a desired climbing road).
4.The gear stability condition is used to find the intermediate gears.
5.The value of cg for relative gear ratios, can be chosen in the range 1≤cg≤2.
To determine the middle gear ratios, there are two recommended methods:
1 - Geometric ratios
2 - Progressive ratios
IV. GEAR BOX RATIO
4.1 Geometric Ratio Gearbox Design
Geometric gearbox: the jump of engine speed in any two successive gears is
constant at a vehicle speed.
The engine’s speed jump is kept constant for any gear change from ni to ni+1
IV. GEAR BOX RATIO
4.1 Geometric Ratio Gearbox Design
A gear-speed plot
for a geometric
gearbox design
IV. GEAR BOX RATIO
4.2 Progressive Ratio Gearbox Design
Progressive gearbox: the speed span of a vehicle in any two successive gears is
kept constant.
IV. GEAR BOX RATIO
4.2 Progressive Ratio Gearbox Design
A gear-speed plot for a progressive gearbox design
IV. GEAR BOX RATIO
4.3 Example 1: A gearbox with three gears
Consider an m = 860 kg car having an engine with η = ηdηg = 0,84 and the powerspeed relationship
We define the working range for the engine, when the power is 100kW ≥ Pe ≥ 90 kW
IV. GEAR BOX RATIO
4.3 Example 1: A gearbox with three gears
The power performance curve and its working range
At the maximum speed vx=50 m/s, the engine is rotating at the upper limit of the
working range ωe = 524 rad/s and the gearbox is operating in third gear.
IV. GEAR BOX RATIO
4.3 Example 1: A gearbox with three gears
The gear-speed plot for a three-gear gearbox
IV. GEAR BOX RATIO
4.4 Example 2: Better performance with a four-gear gearbox
The gear-speed plot