derivation for Power transmission of Vehicle.pptx
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Power TX of Vehicle
derivation for Power transmission of Vehicle.pptx
- 2. Tractive Effort • The torque and rotating speed of the power plant output shaft are transmitted to the drive wheels through the clutch or torque converter, gearbox, final drive, differential, and drive shaft. � � 𝐹 = � � 𝑟 𝑑 = 𝑇 𝑖 � � 𝑖𝑜 𝜂 𝑇 𝑡 𝑝 𝑟 𝑑 ig – Input gear raio io – Output gear ratio Tp – Torque output 𝑟 𝑑 – Wheel radius Nw Tw rd Ft Engin e
- 3. Efficiency • Mechanical Efficiency. • Clutch : 99% • Gear pairs : 95% • Bearing and Joints : 98%
- 4. Speed • The rotating speed (rpm) of the driven wheel, � � � � = 𝑁𝑝 𝑖𝑔𝑖 𝑜 • The translational speed of the wheel centre (vehicle speed) can be expressed as 𝑉 = 𝜂𝑁w𝑟 𝑑 3 0 m/ s 𝑉 = 𝜂𝑁𝑝 𝑟𝑑 30 𝑖$𝑖𝑜 m/ s
- 5. Ideal Characteristics of Power Train • Ideal performance characteristic of a power plant is the constant power output over the full speed range. • At low speeds, the torque is constrained to be constant • It provides the vehicle with a high tractive effort at low speeds, where demands for acceleration, or grade climbing capability are high. Speed Powe r Torqu e
- 6. Characteristics of ICE • IC engine usually has torque– speed characteristics far from the ideal performance characteristic required by traction. • Operates smoothly at idle speed. • Good combustion quality and maximum engine torque are reached at an intermediate engine speed. Torqu e Powe r Specific fuel consumptio n 10 0 30 0 8 0 24 0 6 0 18 0 4 0 2 0 0 1000 2000 3000 4000 5000 Speed (rpm) 31 0 29 0 27 0 Power (kW) Specific fuel consumption (g/kWh) Torque (Nm)
- 7. Characteristics of ICE • As the speed increases further, the mean effective pressure decreases because of the growing losses in the air-induction manifold and a decline in engine torque. • Power output, increases to its maximum at high speed. • At high speed, engine torque decreases more rapidly resulting in decline of engine power output. Torqu e Powe r Specific fuel consumptio n 10 0 30 0 8 0 24 0 6 0 18 0 4 0 2 0 0 1000 2000 3000 4000 5000 Speed (rpm) 31 0 29 0 27 0 Power (kW) Specific fuel consumption (g/kWh) Torque (Nm)
- 8. Characteristics of ICE • The internal combustion engine has a relatively flat torque– speed profile Torqu e Powe r Specific fuel consumptio n 10 0 30 0 8 0 24 0 6 0 18 0 4 0 2 0 0 1000 2000 3000 4000 5000 Speed (rpm) 31 0 29 0 27 0 Power (kW) Specific fuel consumption (g/kWh) Torque (Nm)
- 9. Characteristics of ICE – Multi gear • A multi-gear transmission is usually employed to modify this. 5 4 3 2 1 0 0 20 40 60 80 100 120 140 160 180 200 Vehicle speed (km/h) 1st gear 2nd gear 3rd gear 4th gear Tra c t i v e effort o n w h e e l (k N )
- 10. Characteristics of Electric Motor • Electric motors, usually have a speed– torque characteristics that is much closer to the ideal characteristics. • Electric motor starts from zero speed. • As speed increases to base speed, the voltage increases to its rated value while the flux remains constant. • Beyond the base speed, the voltage remains constant and the flux is weakened resulting in constant output power while the torque Power Torque Base speed 80 70 60 50 40 30 20 10 0 0 1000 400 350 300 250 200 150 100 50 4000 5000 2000 3000 Motor (rpm) Motor power (kW) Motor torque (Nm)
- 11. Transmission Characteristics • The transmission requirements of a vehicle depend on the characteristics of the power plant and the performance requirements of the vehicle. • A well-controlled electric machine such as the power plant of an electric vehicle will not need a multi-gear transmission. • However, an IC engine must have a multi- gear or continuously varying transmission to multiply its torque at low speed.
- 12. Transmission Characteristics •Transmission - all systems employed for transmitting engine power to the drive wheels. •In automobile applications, there are usually two basic types of transmission: • Manual gear transmission • Hydrodynamic transmission.
- 13. Manual transmission • Manual gear transmission consists of a clutch, gearbox, final drive, and drive shaft • The final drive has a constant gear reduction ratio or a differential gear ratio. • The gearbox provides a number of gear reduction ratios ranging from three to five for passenger cars and more for heavy commercial vehicles Engin e
- 14. Manual transmission • Maximum speed requirement of the vehicle determines the gear ratio of the highest gear • Maximum tractive effort requirement of the vehicle determines the gear ratio of lowest gear. • Ratios between them should be spaced in such a way that they will provide the tractive effort– speed characteristics as close to the ideal as possible Speed Ideal tractive effort 1st gear 2nd gear 3rd Gear 4th gear Tractive effort Gear box ratio, 𝑖𝑔1 = 𝑖𝑔2 = 𝑖𝑔3 = 𝑘𝑔
- 15. Manual transmission > > 𝑖𝑔1 𝑖𝑔2 𝑖𝑔3 𝑖𝑔2 𝑖𝑔3 𝑖𝑔4 Gear ration can be obtained by, 𝑔𝑛 − 1 = 𝑖 𝑘𝑔 𝑖𝑔𝑛 Engine operating speed range V4 V3 V2 V1 ne1 Engine speed ne 2 Vehicle speed 1st 2nd 3rd 4th Gear