What is torque?
Torque is the rotational equivalent of linear force. It is a moment of force and produces a turning effect.
Example of Torque: It is easy to loosen or fasten a nut or screw using a long wrench than using a short wrench. The long handle of the wrench adds more perpendicular distance which increases torque applied which makes it easy to do the job.
We can express torque in terms of both force and current.
In standard IC engine cars, torque is a function of force while in electric vehicles it is a function expressed in terms of current.
What makes Electric Vehicle have Instant Torque?
Electric vehicles get instantaneous torque through their motors. Torque in electric vehicles depends on the initial current applied.
To better understand how EVs get instant torque we have to understand the anatomy of the IC engine.
Torque in IC Engine:
Torque has a simple formula given by:
T = Force(F) multiplied by the perpendicular distance (D)
In the IC engine force is acting in perpendicular to distance. The generated force comes from the combustion of a mixture of fuel and air in a fixed ratio. Torque produced is maximum when the fuel mixture produces a maximum perpendicular force.
This procedure is the same in both petrol and diesel engines. The basic difference between petrol and diesel engine is how fuel combustion takes place.
In the petrol engine, the combustion takes place in the cylinder with the help of spark plug, while in diesel engine the combustion occurs by compression of the fuel under high pressure by the piston.
Also, the IC engine has lots of heavy moving parts which needs to be in a proper position before they can start. This is why IC engines are not self-starting. The heavy parts present in the engine like a flywheel, crankshaft increase the inertia which further lowers the starting torque.
Torque in Electric Vehicles:
Unlike IC engines electric motors are very lightweight and robust. It can deliver instant torque. In this scenario, we are considering Brushless DC motor(BLDC) as most of the EVs come equipped with BLDC motor.
As we step on the pedal, the current rushes to the motor which in turn starts rotating the armature. When the vehicle is standing the inertia of motor or Back EMF is nearly zero (the Back EMF opposes the applied voltage). Being back emf zero all the current goes in torque generation, unlike IC engines. Hence the high starting torque is achieved in electric vehicles.
Also read why DC charging is fast in EVs.