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PHYSICS OF HYBRID VEHICLES
Transcript of PHYSICS OF HYBRID VEHICLES
Regenerative braking is a system which charges the vehicle's batteries when braking. In conventional braking systems, the brakes convert all of the vehicle's kinetic energy into heat energy by using friction. This friction comes from the brake lining which, when used, will eventually deteriorate and need to be replaced. However, in a hybrid vehicle, regenerative braking is used. This system allows the kinetic energy to be converted into another energy, which can be stored in the battery or used straight away. The vehicle uses its electric motor as a generator when braking, and the energy is converted into electrical energy, which is then converted into chemical energy by the battery. This transfer of the energy is what slows the vehicle.
Regenerative brakes are used in conjunction with traditional brakes. This is because regenerative brakes only work at slowing the car down and cannot be used to stop the car entirely. Traditional brakes are also needed when braking suddenly or when the regenerative brakes fail.
Regenerative braking can be shown by these formulae:
In a normal vehicle with only a combustion engine, some energy transformations occur. These transformations are similar to those of a hybrid vehicle, but with a few differences. In a traditional vehicle, chemical potential energy from the battery is converted into electrical energy. This energy is converted into magnetic energy in the vehicle's starter, which produces kinetic energy to turn the motor over, thereby starting the engine. In a hybrid vehicle, however, the electric motor receives energy from the battery in order to start the car.
When driving, a normal car is constantly converting chemical potential energy into kinetic energy even when it is driving at a constant velocity because of friction and will do more work when accelerating. A hybrid vehicle does the same but converts electrical potential energy into kinetic energy.
When a hybrid vehicle reaches a high enough speed, the combustion engine will be used alongside the electric motor. This is to provide more power and to charge the batteries. When both motors are running, electrical and chemical energy are being used to spin the wheels and move the vehicle.
Regenerative braking is also a way of transforming energy in a hybrid vehicle.
Uses of electric motors and combustion engines in hybrid vehicles.
Important parts of a hybrid vehicle
How regenerative braking works.
Forces When Driving
When a vehicle is stationary, it has two forces affecting it: weight force and support force. The weight force is the mass of the vehicle multiplied by gravity, which is 10ms-2 on Earth. Weight force is exerted on the whole car while the support force is only on the wheels and the ground; however, these two forces are balanced.
When driving, the same forces apply with the addition of a few more forces. These additional forces include friction, air resistance/drag and push. The push force comes from the wheels as they spin which comes from the driving force of the engine. As the vehicle accelerates, the push force and its opposing forces increase. This is because force is equal to mass times acceleration. For example, if the vehicle is 1,000kg and it is accelerating at 10ms-2, its force will be 10,000N. The opposing forces, friction and air resistance, will not be 10,000N each, but instead will add up to 10,000N. If the vehicle is not accelerating and is instead travelling at a constant velocity, that means the push force and its opposing forces are equal. If the push force is decreased by taking your foot off the accelerator, the friction and air resistance will be greater. This means the vehicle's net force is going backwards meaning the car will eventually slow down. Another way to slow a car would be to increase the opposing forces by braking.
The weight force affects the whole car and is opposed by the support force which is provided by the wheels on the ground.
The push/driving force comes from the engine, which spins the wheels. This is opposed by air resistance and friction.
These forces also apply to hybrid vehicles.
Pros of Hybrid Vehicles
Conserves energy: Hybrids use a motor and an engine to maximise the power.
Regenerative Braking: As explained before, hybrid vehicles can save the energy when braking to use later.
Lighter Weight: Hybrids are made of lighter materials and have a lighter engine. This means that the car doesn't need as much force or energy to move.
Lower power output: Hybrid vehicles are not built to drive fast. The combustion engine is what is needed for higher speeds, however it is smaller meaning less power is produced.
Poorer handling: Hybrids don't handle as well as conventional vehicles because they are stripped of as much weight as possible. The weight is also distributed very poorly. The most weight is at the front and the back of the vehicle for the engine/motor and batteries respectively.
Cons of Hybrid Vehicles
In automatic vehicles, gas and hybrid, there are two pedals: one for the brake and one for the accelerator. In both vehicles the two pedals are very similar.
The accelerators in both vehicles use almost exactly the same systems. When the pedal is pressed, it converts the pressure that you apply into an electric signal. It sends this signal to a potentiometer or a Hall effect sensor. These then control the power produced by the motor/engine.
The braking system is much different to the accelerator. The brakes use a mechanism known as hydraulic brakes. When the brake pedal is pressed, the force applied becomes pressure in the non-compressible brake fluid. The pressure comes from the small piston connected to the pedal. The brake fluid is pushed towards a larger piston which converts the pressure into a much larger force than originally exerted. This force then goes on to the brakes.
Force is measured in Newtons (N)
Force is equal to mass multiplied by acceleration.
Weight force is equal to mass multiplied by acceleration due to gravity.
Push force is the amount of force you exert toward an object. In a vehicle, this can be seen by the wheels pushing the ground in order to move the car.
Friction is a force that opposes other forces. Friction occurs more in rougher objects. The tread on the tyre is designed to give the vehicle more traction, which also gives it more friction. If a car tyre had no tread, it would give less friction.
Air resistance, also known as drag, is a force that is relative to the velocity of an object. When an object is more streamline, there is less drag.
Support/reaction force follows Newton's Third Law of Motion:
"every action is attended by an equal and opposite reaction".
This means that there is equal and opposite force on any object with a weight.
Weight force is the downward force caused by gravity. On Earth the weight force is the mass of an object multiplied by 10, because Earth's gravity is 10ms-1
Other Hybrid Features
Hybrid vehicles also have a few other important features.
One of these features is electric motor drive/assist. This feature is used to provide more power to the vehicle in acceleration, passing, and driving uphill. This feature is used to make less power be used in the combustion engine. This means that there is less fuel being burned and more renewable energy being used.
Automatic start/shut off is another feature in hybrid vehicles. This automatically turns off the combustion engine and turns it back on when you accelerate. This is also to save fuel.
What these formulae say is that the energy produced by the regenerative brakes is equal to the efficiency of the battery (power out divided by power in), multiplied by the efficiency of the generator (work out divided by work produced), multiplied by mass and velocity squared. The result is then divided by 2.
In order to increase the energy produced by the brakes you must:
increase the efficiency of the battery,
increase the efficiency of the generator,
increase the mass of the vehicle, or
increase the velocity of the vehicle.
Hybrid cars have existed since the early 20th century; however they are only recently becoming more abundantly seen on the roads. They are similar to petrol cars, but instead use both petrol and electricity. This does have some pros and cons because both different types of vehicle have different physics involved, such as forces and energy transfers.
There are many different types of hybrid cars, each with different configurations of their engines and batteries which gives each vehicle different advantages.
The types of hybrid cars are:
Parallel - Has an electric motor and a combustion engine. Uses the engine and motor when in combustion mode but only uses the electric motor when in electric mode.
Mild Parallel - Uses a small electric motor, which charges when braking, to assist the vehicle in accelerating, starting, and stopping.
Series-Parallel - Has an electric motor and a combustion engine. The motor and engine can be used at different percentages and the engine can also be used to charge the motor.
Series - Uses an electric motor in order to drive, and the engine is connected to a generator which charges the batteries.
Plug-in - The same as a parallel or series hybrid but has a larger battery and can be plugged in to charge.
As seen in this example, the force applied on the brakes is 400N. This force goes to the piston which has an area of 5cm squared. This creates 800,000Pa of pressure because of the formula:
Pressure equals force divided by area.
The pressure presses against the 60cm squared piston which then exerts a force of 4800N; 12 times greater than the original force exerted.
The Power Split Device is the vehicle's gearbox
By Jolon Behrent