How Does A Car Work?

Document Sample
How Does A Car Work? Powered By Docstoc
					                                   How Does A Car Work?

Systems Realization Laboratory
                                               Chris Paredis

                                 G.W. Woodruff School of Mechanical Engineering
                                         Georgia Institute of Technology
                 Learn More about Cars

 The graphical material in this lecture is copied from
  www.howstuffworks.com
 You can find much additional information at this web-site




                                              Systems Realization Laboratory
           Car Sub-Systems of Interest

                          Transmission
  Engine
                                                        Tires




Car
Body



              Torque Converter                               Differential



                                         Systems Realization Laboratory
Engine




         Systems Realization Laboratory
                Four Cycles




Intake   Compression   Combustion                 Exhaust




                                Systems Realization Laboratory
                                                                                                                                                             Engine Power as a function of Engine Speed
                                                                                                                                             450
                               Engine Torque as a function of Engine Speed                                                                                                                        Chevy 4-cyl 1.8L
               1400                                                                                                                                                                               Ford 6cyl 3L
                                                                                                                                             400


               1200
                                                   Simplified Engine Model
                                                                    Chevy 4-cyl 1.8L
                                                                    Ford 6cyl 3L
                                                                    Porsche 8cyl 5.4L                                                        450
                                                                                                                                             350
                                                                                                                                                                                                  Porsche 8cyl 5.4L
                                                                                                                                                             Engine Power as a function of Engine Speed

                                                                                                                                                                                                   Chevy 4-cyl 1.8L
                               Engine Torque as a function of Engine Speed                                                                   400                                                   Ford 6cyl 3L
                                                                                                                                             300


                                            f ( )
                                                                                                                                                                                                   Porsche 8cyl 5.4L


                                                                                                                                                                         P  
               1000
               1400
                                                                                                                                                             Engine Power as a function of Engine Speed
                                                                    Chevy 4-cyl 1.8L




                                                                                               Power [kW] Power [kW] Power [kW] Power [kW]
                                                                                                                                             350
                                                                                                                                             450
                                                                                                                                             250
                                                                    Ford 6cyl 3L
                                                                                                                                                                                                    Chevy 4-cyl 1.8L
Torque [Nm]




               1200
                800                                                 Porsche 8cyl 5.4L
                                                                                                                                             300
                                                                                                                                             400
                                                                                                                                             200                                                    Ford 6cyl 3L
                                                                                                                                                                                                    Porsche 8cyl 5.4L
                               Engine Torque as a function of Engine Speed                                                                                          Power as a function of Engine Speed
                                                                                                                                                             Engine Torque as a function of Engine Speed
               1000
                600
               1400                                                                                                                          1400
                                                                                                                                              250
                                                                                                                                              450
                                                                                                                                              350
                                                                                                                                              150
                                                                    Chevy 4-cyl 1.8L                                                                                                               Chevy 4-cyl 1.8L
                                                                    Ford 6cyl 3L                                                                                                                   Ford 6cyl 3L
                                                                                                                                              200
                                                                                                                                              400
                                                                                                                                              300
                                                                                                                                              100
Torque [Nm]




                800
                400
               1200                                                 Porsche 8cyl 5.4L                                                        1200                                                  Porsche 8cyl 5.4L

                                                                                                                                             150
                                                                                                                                             350
                                                                                                                                             250
                                                                                                                                              50
                600
                200
               1000                                                                                                                          1000
                                                                                                                                              100
                                                                                                                                              300
                                                                                                                                              200
                                                                                                                                                0
                                                                                                                                               1000   2000      3000       4000     5000        6000      7000          8000




                                                                                               Torque [Nm]
 Torque [Nm]




                400
                  0
                800                                                                                                                          800                            Speed [RPM]
                 1000   2000      3000       4000     5000       6000        7000       8000                                                  50
                                                                                                                                             250
                                                                                                                                             150
                                              Speed [RPM]
                200
                600                                                                                                                            0
                                                                                                                                             200
                                                                                                                                             100
                                                                                                                                             600
                                                                                                                                               1000   2000       3000      4000     5000        6000       7000         8000
                                                                                                                                                                            Speed [RPM]
                                                                                                                                             150
                                                                                                                                              50
                  0
                400                                                                                                                          400
                 1000   2000       3000      4000     5000       6000        7000       8000
                                              Speed [RPM]                                                                                    100
                                                                                                                                               0
                                                                                                                                               1000   2000       3000      4000     5000        6000       7000         8000
                200                                                                                                                          200                            Speed [RPM]
                                                                                                                                              50

                 0                                                                                                                             0
                 1000   2000       3000      4000     5000        6000       7000       8000                                                   1000   2000       3000      4000     5000        6000       7000         8000
                                              Speed [RPM]                                                                                                                   Speed [RPM]



                               Use SI units! Torque in [Nm], velocity in [rad/s] and Power in [W]


                                                                                                                                                                  Systems Realization Laboratory
           Car Sub-Systems of Interest

                          Transmission
  Engine
                                                        Tires




Car
Body



              Torque Converter                               Differential



                                         Systems Realization Laboratory
Torque Converter




                   Systems Realization Laboratory
                  Torque Converter




The model of a torque converter is fairly complex and highly nonlinear
                We will not consider it in this class.
    If you need it, it will be provided to you as a Matlab function.



                                                  Systems Realization Laboratory
           Car Sub-Systems of Interest

                          Transmission
  Engine
                                                        Tires




Car
Body



              Torque Converter                               Differential



                                         Systems Realization Laboratory
                                         Transmission
 Purpose: provide large power at all vehicle velocities
                                        Power at the drive shaft for different gear ratios
                         250




                         200




                         150
            Power [kW]




                         100




                         50




                          0
                               0   50      100       150        200       250      300         350     400
                                                           Velocity [kmh]



                                                                                             Systems Realization Laboratory
Transmission




                                   sun
                planet                        ring


       more
      compact




                 Systems Realization Laboratory
                      Model of a Transmission
 Assumptions:
    •   No friction or other losses
    •   No inertia

 Reduces the rotational velocity:
                      in
           out 
                        n
 Increases the torque

           out   in  n
   where n is the transmission ratio and subscript in refers to the shaft
   connected to the torque converter.



                                                    Systems Realization Laboratory
           Car Sub-Systems of Interest

                          Transmission
  Engine
                                                        Tires




Car
Body



              Torque Converter                               Differential



                                         Systems Realization Laboratory
Differential




               Systems Realization Laboratory
Model of a Differential – Same as Transmission
 Assumptions:
    •   Car drives in a straight line
    •   No friction or other losses; no inertia

 Reduces the rotational velocity:
                       in
           out 
                         n
 Increases the torque

            out   in  n
   where n is the transmission ratio and subscript in refers to the shaft
   connected to the transmission.



                                                    Systems Realization Laboratory
                           Model of a Wheel
 Assumptions:
   • Car drives in a straight line
   • No slip; no tire deformation; no friction losses; no inertia

 Converts rotational velocity into translational velocity:

       vcar  Rwheel

 Converts torque into force:
                  wheel
       Fcar 
                    R
  where R is the radius of the wheel.


                                                           Systems Realization Laboratory
                     Model of the Car Body

                                                                         Fdrag
 Wind Resistance:
                                          Fgrav
             1
    Fdrag    Cd  A(vcar )2
             2                 Frolling
 Gravitational Force:                    
    Fgrav  mg sin( )
                                                               mg cos( )
 Tire Resistance:

    Frolling  r mg cos( )
                                                   mg



                                                  Systems Realization Laboratory
                                Putting It All Together
                                         Engine and Load Torques for a 10% Slope
                 300




                 250



                                            engine torque
                 200                        load torque (1st)
                                            load torque (2nd)
torque in [Nm]




                                            load torque (3rd)
                                            load torque (4th)
                                            load torque (5th)
                 150




                 100




                  50




                  0
                  1000   2000     3000    4000       5000      6000      7000      8000    9000    10000
                                                   engine speed in rpm



                                                                                   Systems Realization Laboratory
Examples of Other Models in Vehicle Design

Computational Fluid Dynamics
                                                           Noise, Vibration,
                                                           and Harshness




  Thermal                                               Crash Testing
                           Stress Analysis




                                             Systems Realization Laboratory

				
DOCUMENT INFO
Shared By:
Categories:
Tags: Does, Work?
Stats:
views:2
posted:4/9/2012
language:English
pages:20