Automobile transmission system
Vehicle Design
Transmissions Part 1
Dr. Alasdair Cairns
Content
•
Transmission fundamentals
– Principles of gears (revision)
– Road load losses
•
Gear ratio optimisation
– Performance
– Fuel economy
Transmissions – Overview
Why do we need a gearbox in a road car?
Transmissions – Practical Use
Seven practical reasons why a gearbox is required: 1. To increase tractive effort when the vehicle is moved from rest
2. To improve hill climbing or descending ability
3. To allow the engine to be operated near to peak torque during vehicle acceleration
4. To allow the engine to be operated near to peak power at the required maximum vehicle speed (“Vmax”)
5.
5 To allow the engine to be operated at the most efficient point for a given vehicle speed (within the gear ratios available)
6. To avoid engine stall at low vehicle speeds
7. To allow the vehicle to be easily driven in either forward or reverse direction
4
© MAHLE
Transmissions – Mechanical Leverage (1)
P T
where:
P is power (W)
T is torque (Nm)
is angular velocity (rad/s)
•
Engine speed ranges are typically limited to 850-7000rpm
•
Required wheel speeds are 0-1800rpm (road car) or 0-2500rpm (F1)
•
When the speed is too low or the load too g p great the engine stalls g •
The primary function of the gearbox is therefore to maintain the optimum torque and engine speed for a given vehicle condition, within the engine speed range:
1.
1 For a given engine power by gearing down the wheel speed we can increase the available power, torque at the road wheel
2. By gearing up the wheel speed we can effectively widen the speed range available….
4
© MAHLE
Transmissions – Mechanical Advantage (2)
P1 P2
Driver
(G1)
•
•
•
•
4
Driven
(G2)
T1 1 T2 2
Mechanical Advantage refers to an increase in torque or force that a mechanism achieves g q through power transmission
Power is the
Transmissions Part 1
Dr. Alasdair Cairns
Content
•
Transmission fundamentals
– Principles of gears (revision)
– Road load losses
•
Gear ratio optimisation
– Performance
– Fuel economy
Transmissions – Overview
Why do we need a gearbox in a road car?
Transmissions – Practical Use
Seven practical reasons why a gearbox is required: 1. To increase tractive effort when the vehicle is moved from rest
2. To improve hill climbing or descending ability
3. To allow the engine to be operated near to peak torque during vehicle acceleration
4. To allow the engine to be operated near to peak power at the required maximum vehicle speed (“Vmax”)
5.
5 To allow the engine to be operated at the most efficient point for a given vehicle speed (within the gear ratios available)
6. To avoid engine stall at low vehicle speeds
7. To allow the vehicle to be easily driven in either forward or reverse direction
4
© MAHLE
Transmissions – Mechanical Leverage (1)
P T
where:
P is power (W)
T is torque (Nm)
is angular velocity (rad/s)
•
Engine speed ranges are typically limited to 850-7000rpm
•
Required wheel speeds are 0-1800rpm (road car) or 0-2500rpm (F1)
•
When the speed is too low or the load too g p great the engine stalls g •
The primary function of the gearbox is therefore to maintain the optimum torque and engine speed for a given vehicle condition, within the engine speed range:
1.
1 For a given engine power by gearing down the wheel speed we can increase the available power, torque at the road wheel
2. By gearing up the wheel speed we can effectively widen the speed range available….
4
© MAHLE
Transmissions – Mechanical Advantage (2)
P1 P2
Driver
(G1)
•
•
•
•
4
Driven
(G2)
T1 1 T2 2
Mechanical Advantage refers to an increase in torque or force that a mechanism achieves g q through power transmission
Power is the