There are two limiting factors to the maximum tractive effort of the vehicle: A maximum tractive effort that the tire-ground contact can support Tractive effort that the maximum torque of the power plant can produce with the given driveline gear ratios. The smaller of these factors will determine the performance potential of the vehicle. Usually it is the second factor that limits the vehicle's performance.

In selecting a suitable power plant, the following factors are considered: Operating performance Economy Environment friendliness For vehicular applications, the ideal performance characteristic of a power plant is constant power output over the full speed range. Consequently, the torque varies hyperbolically with respect to speed. This ideal performance characteristic of the power plant will ensure that the maximum power is available at any vehicle speed, thus resulting in optimal vehicle performance. In practice, however, the torque is constrained to be constant low speeds. This is done so as not to be over the maxima limited by the adhesion between the tyre-ground contact areas. The internal combustion (IC) engines are the most commonly used power plants for land vehicles. In hybrid and electric vehicle technology, the electric motor is used.  

Internal combustion engine The internal combustion engines used in the vehicles are based on two principles: spark ignition (petrol engines) principle Diesel principle. The key features of the ICs based spark ignition principle are: high power/weight ratio good performance low combustion noise.

The disadvantages of are the ICs based spark ignition principle are: quality of fuel required higher fuel consumption. The advantages of the diesel engines are: low fuel consumption low maintenance requirement due to the absence of ignition system low fuel quality required The disadvantages of the diesel engine are high level of particulate emission greater weight and higher price higher levels of noise The two typical characteristic curves used to describe the engine characteristic are: torque vs. engine speed curve at full load (100% acceleration pedal position) power vs. engine speed curve at full load (100% acceleration pedal position)

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