Whilst driving a vehicle with a regenerative braking system, the electric motor draws power from the battery to turn the wheels, creating the kinetic energy it needs to move. When the brakes are applied however, the process switches into reverse mode. Now the kinetic energy that was initially used to propel the vehicle, makes the wheels rotate the electric motor, turning it into a type of generator. The electrical energy is then stored in a high voltage battery, where it is used again to help propel the vehicle.
Yet, when it's travelling at high or very low speeds, is stationary or the battery is fully charged, too hot or too cold, the electric motor cannot provide enough braking torque on its own and will need the support of a hydraulic braking system. To what extent will largely depend on the vehicle. Because the hydraulic brakes are essentially a back-up system, they are used less, and in theory should last longer. So, the key braking components still wear - just differently. Electric vehicles EVs run primarily off the charge they stored when plugged into an outlet, but use regenerative braking to help top up the battery.
In addition to the regenerative system, all electrified vehicles have conventional braking systems as regular vehicles do.
These use metal discs, called rotors, that are located behind the wheels and which turn with them. When you press the brake pedal, the pressure of hydraulic fluid squeezes metallic brake pads tightly against the rotors, and the resulting friction slows the car. That friction converts kinetic energy to thermal energy, and the brakes get hot. The idea behind regenerative braking is to capture that otherwise-wasted kinetic energy and put it to use, converting it to electricity.
With an electrified vehicle, the electric motor drives the wheels, either in conjunction with the gasoline engine as in a hybrid, or on its own in a battery-electric vehicle. As you drive forward, the motor runs in that direction, supplying electric power to the wheels. But when you decelerate by taking your foot off the throttle, the electric motor stops supplying power so the vehicle will slow down. When the motor stops, it immediately disengages, and then starts running backwards.
It captures the kinetic energy from the wheels as they slow down, and converts it into electricity. In gas powered vehicles, the electricity can be used to power the cars electronics or sent to a battery where it can later used to give the vehicle an extra boost of power. This technique is currently used in some Le Mans Prototype racing cars. In flywheel RBS, the system collects the kinetic energy of the vehicle to spin a flywheel that is connected to the drive shaft through a transmission and gear box.
The spinning flywheel can then provide torque to the drive shaft , giving the vehicle a power boost. Electro flywheel regenerative brake is a hybrid model of electromagnetic and flywheel RBSs. It shares the basic power generation methods with the electromagnetic system; however, the energy is stored in a flywheel rather than in batteries.
In this sense, the flywheel serves as a mechanical battery, where electrical energy can be stored and recovered. The spring loaded regenerative braking system is typically used on human powered vehicles, such as bicycles or wheelchairs. In spring RBS, a coil or spring is winded around a cone during braking to store energy in the form of elastic potential.
The potential can then be returned to assist the driver while going up hill or over rough terrain. The hydraulic RBS slows the vehicle by generating electricity which is then used to compress a fluid. Nitrogen gas is often chosen as the working fluid. Hydraulic RBSs have the longest energy storage capability of any system, as compressed fluid does not dissipate energy over time.
However, compressing gas with a pump is a slow process and severely limits the power of the hydraulic RBS. Modern hybrid and electric cars both utilize an electric engine to power the car which makes applying regenerative braking very simple and efficient.
In the vast majority of these cars, the transmission of the car is set up such that when the driver applies the brakes, the electric motor reverses itself and applies a resistance to the wheels rather than power. The resistance applied to the wheels is then put through the electric motor where it is used to recharge the batteries. In high performance electric cars, improving the feel of the car is very important to car manufacturers. Many customers support electric super-cars but are against purchasing them because of the lack of high performance feel.
One important aspect of this feel is engine braking. All of that energy was simply lost to the environment. Fortunately, we have evolved as a species and developed a better way. Then, the next time the car accelerates, it uses much of the energy previously stored from regenerative braking instead of tapping in further to its own energy reserves. Basically, the most efficient way to drive any vehicle would be to accelerate to a constant speed and then never touch the brake pedal.
Since we need to brake often, regenerative braking is the next best thing. It takes the inefficiency of braking and simply makes the process less wasteful. To evaluate regenerative braking, we really need to look at two different parameters, efficiency and effectiveness. Despite sounding similar, the two are quite different. Does it waste a lot of energy as heat, or does it turn all of that kinetic energy back into stored energy?
Effectiveness, on the other hand, refers to how large of an impact regenerative braking really makes. Does it measurably increase your range, or will you not notice much of a difference? This is fairly standard across most electric vehicles including cars, trucks, electric bicycles, electric scooters, etc. What should interest us more is the effectiveness of regenerative braking. This is where things get really interesting.
0コメント