Traction Theory

Tractive force also known as traction is referred to as a force that is utilised for generating motion between a surface that is tangential in nature and a body. This force is often created through the utilisation of shear force and utilisation of dry friction. In simple words, traction can be defined as the maximum force of traction between a surface and a body, which is often limited by the available friction. If this happens then traction is often represented in the form of a ratio between Tractive force and normal force and is known as the traction coefficient. This is quite similar to the friction coefficient. 

Traction theory

The traction theory mostly involves the concept of traction. It is essentially a physical process that involves the transmission of tangential force over an interface in between 2 bodies through a film of intervening fluid or dry friction resulting in power transmission, stoppage of motion. However, in-vehicle dynamics there is a close relation between tractive force, drawbar pull, and tractive effort, although the 3 mentioned terms have different definitions. 

Traction Theory formula

In Traction theory, the traction coefficient is also important, which is described as the usable traction force divided by the specific weight over the running gears? Hence, the Traction theory formula or the formula for usable traction is given by 

The traction that is usable = normal force * traction coefficient. 

Several factors affect the traction coefficient. In this context, it should be mentioned that traction present between two particular surfaces is dependent on various factors. These have been outlined in the following. 

• Each surface’s material composition. 
• The normal force is pressing the surface of contact together.
• Microscopic as well as macroscopic shape.
• Contaminants at the boundary of the material involve adhesives and lubricants. 
• Traction direction concerning a specific system of coordinates. For instance, the traction that is available within a tire is often variable in between braking, accelerating, and cornering. 
• A Tractive surface’s relative – an object that is a non – sliding has more traction as compared to an object that is sliding in nature.
• For different surfaces such as ice or off-road that are low friction in nature, traction can be raised through the utilisation of traction devices that penetrate the surface partially. Instead of solely relying on dry friction, these devices utilise the underlying surface’s shear strength In this regard some examples such as snow chains or aggressive off-road tread can be mentioned.

Traction Theory Examples

Throughout engineering, several examples of traction force can be viewed. These have been presented in the following.

Example 1: Find a tractor wheel’s tractive force which works with a 5kN dynamic force on particular firm soil. The tractive efficiency and wheel velocity are 0.73 and 2ms-1 respectively Calculate the power that must be transferred to the axle of the wheel. 

Solution: Let equivalent friction coefficient be 0.48 and the firm soil’s mean value is 0.43 – 0.53. Then the tractive force is given by H = Wµ = 5 * 0.48 = 2.4 kN.

Now, calculating the tractor wheel’s tractive power we get PW = vaH = 2 * 2.4 = 4.8 kW. 

Next the power which must be transferred to the axle wheel for utilising equation Re – Fr = 0, with the provided tractive efficiency is calculated as PW = Pt / TE = 4.8 / 0.73 = 6.58kW.The value of the required power can be utilised for designing several components of power transmission. The consumption of power can be further utilised to compute the ultimate power source’s power demand, maybe an engine for calculating fuel consumption and in turn cost of a particular operation.

Example 2: A wheel is working with a 10kN dynamic load, having a 0.08 motion resistance ratio and 0.72 as the ratio of gross traction ratio. Calculate the traction force. 

Solution: The gross force of traction is developed by the specific wheel F by utilising the equation 

F = Wµg = 10 * 0.72 = 7.2 kN

The motion resistance Fr is calculated as Fr = Wρ = 0.08 * 10 = 0.80kN.

The developed tractive force the developed by the specific wheel is the value of subtraction of motion resistance from the gross force of traction that is 

H = F – Fr = 7.2 – 0.8 = 6.4kN.

Conclusion 

The overall article has been written on the core topic of traction theory. Traction theory is a vital concept in Agricultural engineering and involves the concepts of traction. This topic has been further analysed through discussion of traction theory formulas and traction theory examples.