This document discusses continuous variable transmissions (CVTs). It begins by explaining the basic function of a transmission to change the speed ratio between an engine and wheels. It then discusses problems with manual and automatic transmissions. The benefits of a CVT are that it provides constant engine torque optimization and improved fuel efficiency through a continuously variable transmission ratio. The main types of CVTs are pulley-based, toroidal, and hydrostatic. Pulley-based CVTs vary the gear ratio by adjusting the distances between two pulley sheaves. Toroidal and hydrostatic CVTs use different mechanisms to provide a continuous range of transmission ratios. The document concludes by discussing CVT control systems and advantages/disadvantages of

1. CONTINOUS VARIABLE TRANSMISSION
C V T
BY : Ziad Zohdy

2. Basics of Transmission
• The job of the transmission is to change the
speed ratio between the engine and the wheels of
an automobile
• The transmission uses a range of gears -- from
low to high -- to make more effective use of the
engine's torque as driving conditions change. The
gears can be engaged manually or automatically.

3. Problems in manual & automatic
transmission

4. Benefits of CVT
 Provide engine torque in optimum condition (road
loads / drive shaft torque)
 No shift clonk
 Transmission ratio can be adjusted continuously
 Better acceleration
 Improved fuel efficiency

5. Behavior of CVT

6. CVT MAIN TYPES
 Pulley based CVT
 Toroidal CVT
 Hydrostatic CVT

7. Pulley based CVT
 The gear ratio is changed by moving the two sheaves
of one pulley closer together and the two sheaves of
the other pulley farther apart.
 The distance between the pulleys does not change
 and neither does the length of the belt
 so changing the gear ratio means both pulleys must
be adjusted (one bigger, the other smaller)
simultaneously in order to maintain the proper amount
of tension on the belt.

8. Pulley based CVT

9. Toroidal CVT

10. Toroidal CVT

11. Hydrostatic CVT
 Power transmitted by hydraulic fluid
 variable displacment pump
& hydraulic motor
• Rotational
motion
ENGINE
• Fluid flow
HYDROSTATIC
PUMP
• Rotational
motion
HYDROSTATIC
MOTOR

12. Hydrostatic CVT
 often,hydrostatic transmission is combined with a
planetary gearset and clutches to create a hybrid system
known as a hydromechanical transmission.
 Hydromechanical transmissions transfer power from the
engine to the wheels in three different modes
 At a low speed power is transmitted hydraulically
 at a high speed, power is transmitted mechanically
 Between these extremes, the transmission uses both
hydraulic and mechanical means to transfer power.
 Hydromechanical transmissions are ideal for heavy-duty
applications, which is why they are common in agricultural
tractors

13. CVT Control

14. Mathematical Model of CVT
 Ie :engine inertia
 Is :active cvt pulley inertia
 Iq :passive cvt pulley inertia
 Be,Bs,Bq:damping coefficient
 i : speed ratio of cvt
 n : transmission efficiency
 Tr : resistance torque of
car weight & load converted
to cvt output

15. ADVANTAGES OF CVT
 Decreases engine fatigue
 Maintains the engine for an optimum power output
 Best acceleration
 More mechanical efficient than the automatic
transmission
 Improved fuel efficiency

16. DISADVANTAGES OF CVT
 Limited torque when compared with manual
 Larger and more costly than automatic or manual
transmission
 Slipping in the drive belt or pulleys

17. In conclusion

18. REFRENCES
 http://www.synchrotronic.com/
 http://auto.howstuffworks.com/cvt.htm
 http://www.wipo.int/pctdb/en/wo.jsp?IA=WO20070
47352&wo=2007047352&DISPLAY=CLAIMS
 www.wikipedia.com

19. BY : ZIAD ZOHDY
THANK YOU 