TRACTIVE EFFORTS

Introduction:
                The term tractive effort is often qualified as starting tractive effort, continuous tractive effort and maximum tractive effort.

Definition:
                Tractive effort is the amount of force in foot- pounds that the motive power must produce to move a train without slipping the wheels. The term "drawbar pulls" is seldom used when talking about motive power. It is the force required to move the entire train except for the motive power equipment being used to pull the train. Tractive effort is simply the sum of the drawbar pull plus the force required to move that motive power equipment itself; locomotive or mobile railcar mover.

Calculation:
The traction F _Z,B required at the drive wheels is made up of the driving resistance forces  is defined as

F_Z,B = F_R F_St F_L F_a

This may be expanded to,

                F_Z,B = m_Fg (f_Rcosα_St sinαSt)   ρ_Lc_WAν²/2 m_Fλa

With steady state motion (a = 0) and the approximations mentioned (cos α St≈1and sinα St≈tanα St) this simplifies to,

F_Z,B = m_Fg (f_R tanαSt)   ρ_Lc_WAν²/2

 

This may be used to calculate the power requirement

P_Z,B = F_Z,Bν

 Figure shows the individual components of driving resistance of a mid-size passenger car, the resultant traction requirement and the power requirement.

 

Fig: Traction required and the resultant power required for a mid-size passenger car

 

 

Taking into account the powertrain ratioi_A and the overall powertrain efficiencyη_tot, the traction F_Z,A available at the wheels may be calculated from the engine characteristic curve.