What is Regenerative Braking in Hybrid Cars

When I was shopping for a hybrid, I had no idea how regenerative braking worked or why I should care about it.  It sounded foreign to me.  How could the slowing down of a vehicle generate electricity?  It does happen with most hybrids.  You can actually charge the battery pack for the electric motor by using kinetic energy.  Gas cars just let this energy disappear into the atmosphere.

What is regenerative braking in hybrid cars?  Regenerative braking converts kinetic energy into a current that is transferred to the battery pack that supplies power to the electric motor in a hybrid car.  Regular brakes lose this energy because it is converted into heat by brake pads. This heat is released into the atmosphere.

When does regenerative braking occur?

Since all owners would like to extend the distance that they can travel on a charge, regenerative braking is the perfect solution.  Certain conditions have to be met in order to initiate the production of current that will charge the hybrid battery network.  Here are the various situations where regenerative braking is occurring:

  1. For my plug-in Sonata hybrid, as soon as I release my foot from the accelerator, the dashboard indicates that the battery pack is being charged, in other words, regenerative braking is happening.
  2.  Some people feel that regenerative braking only happens when you apply the brakes.  This is not so.  Nevertheless, as soon you start to apply the brakes, the level of regenerative braking taking place is a lot higher than it is when you are just coasting along without the use of the ‘gas’ pedal.
  3. Another situation when regenerative is almost optimal is when you are descending a hill.  It will take more power to climb the hill.  Climbing a large hill might even cause the combustion engine to kick in because of the need of a lot of torque.  I hate when this happens within a city because I try my best to stay in electric mode within city limits.
  4. Within a city, while waiting at an intersection, creeping ahead if the car in front you creeps ahead, will charge your battery pack.  Usually, at an intersection, you just simply need to take your foot off of the accelerator to move forward a few inches.  When doing so in a gas car, you are just wasting gas especially if you need to push on the gas pedal to move ahead a few feet.

What processes happen with respect to regenerative braking?

The stop and go requirements in city driving drives a lot of people bonkers.  It is the main reason that people hate city driving.  Once you have a hybrid, you will begin to enjoy all of the opportunities to come to a dead stop.  It will almost become a game for you.

After purchasing my hybrid, I quickly realized that I needed to do some research.  I needed to find out exactly how to ensure that I was using regenerative braking as much as possible.  I had read that you could actually recharge the battery pack to increase the distance that you can travel on one charge as much as 30 percent.  I was ready for the challenge.  Here is what I found out about ins and outs of generative braking.

First of all, I will discuss why normal braking wastes a lot of energy.  

When you use brake pads to stop, the momentum that had been built up is turned into heat.  Your car does not have a way to reuse this energy.  It is not as if you can slap a few eggs on the brake pads to cook some sunny side up eggs for your morning breakfast.

Heat is Lost with Regular Brakes

The heat just leaves the brake shoes and it is lost into the atmosphere.  On the other hand, we have generative braking, it will turn this kinetic energy in a current that is used to charge up your battery pack for the electric motor.

At first, when I had heard about regenerative braking, I thought that it was a fancy braking system that was also used in trains and other vehicles that can travel at high rates of speed that create tons of energy due to momentum.  In actuality, there are no major components that are involved.

Electrical Circuits Are Turned off

Once you start to slow down, the main computer senses that the speed is being reduced and it tells some circuits to stop sending power to the motors.  Now, the electric motor will start to act like a generator and turn the kinetic energy into a current that can be stored in the battery pack.

At first, when you apply the brakes while the current is being created, you still will not use your normal brakes.  At this point, an even higher level of the energy is converted into an electrical current.  Eventually, you will need to come to a complete stop.  That is when the normal friction brakes will kick in.

Why Friction Brakes Kick In

Hybrids have friction brakes just in case the regenerative system was to fail.  Also, if you need to stop quickly, it takes a lot more power than regenerative braking can push out.  I have heard that there are hybrid models that will allow you to come to a complete stop with solely the use of the regenerative braking system.  Nevertheless, my Sonata is not able to do so.

Sometimes if I am on a slight incline, I can almost come to a complete stop; however, I can sense that the regular brakes are kicking in at the last second. You will develop a feel when the regenerative braking is happening.  Also, most hybrids display when this process is taking place.

Even though you might not be saving a ton of money on electricity due to each short trip, all of the incidences when you are able to slow down to almost a complete stop using regenerative braking will add up.

Wind and Temperature Can Affect Kinetic Energy Build Up

One can somewhat control when regenerative braking occurs. Nevertheless, there are factors that you cannot control.  For instance, wind and temperature can affect the amount of kinetic energy that is produced. In a car, if the pavement is high in temperature, it is going to have an effect on your tires causing your vehicle to spin its wheels at a slightly slower rate.

Also, the added friction due to wind conditions can push back on the vehicle if the wind direction is directly on the front of the vehicle.   For instance, we all have experienced the need of using more of the accelerator during times when the wind speed was high in order to maintain a constant rate of speed.

The Electric Motor’s Ability to Convert Kinetic Energy Is Limited

In addition to weather and road conditions, there is another variable that can affect the ability of a hybrid to convert the kinetic energy into a current.  The electric motor’s strength level has its limitations when it is acting as a generator during regenerative braking.

It is not going to be more powerful than it is when it is functioning as a motor that spins the wheels during regenerative braking.  I have read that the electric motor, doing regenerative braking, can convert about 70 percent of the total kinetic energy into a current.  This is definitely much better than a gas motor that cannot use any of the kinetic energy to extend the hybrid’s driving range.

How should you drive so that you maximize the use of regenerative braking?

The coolest challenge that I have discovered with a hybrid is trying to recharge my battery pack as much as possible using regenerative braking.  If you are naive about when regenerative braking happens, you are going to probably underutilize this feature in your hybrid.

If you are not able to extend the range that you can drive, you are going to suffer range anxiety most likely, even within city limits. Range anxiety is at its highest level when you are a newbie to a hybrid.  I personally was not terribly worried since I was ok with allowing my gas motor to be used from time to time.  I was so used to paying for gas on a weekly basis.  If I still had to fill up at the gas pump once a month because I was not extending my driving range enough, I could have dealt with that.

Now, I am able to use the maximum amount of regenerative braking because I learned the few simple tactics to use to make sure that you are charging the electric battery pack even during short trips within the city.

Drive Like a Granny to Initiate Regenerative Braking More Often

The first tactic that I use is to drive like a granny.  Crawl to a stop at stop lights.  I used to go almost full speed and then slammed on the brakes at the last second.  I was one of those fools that thought that I was saving time and getting places faster even during a traffic jam.

Crawling to a stop will activate the generative braking.  What I do is instead of braking, I let go of the accelerator pedal when I am approaching a stop light.  The people behind me are most likely getting frustrated with my cautious way of driving, but I am ok with that.  I do not know them, and if they become frustrated and try to zip around me, they will be forced to wait at the red light anyhow.  They might end up saving five seconds in total by aggressively driving within city limits.

Accelerate Slowly When Light Turns Green

Now that those behind you are frustrated by your way of approaching an intersection, it is time to accelerate once the light turns green.  You have to keep the car in EV mode in order to be able to use regenerative braking, so do not slam your foot onto the accelerator.   This is exactly what I was doing the first few days in my Hybrid.  I was speeding up as quickly as possible thinking that I was going to arrive at my destination faster.

When you over-accelerate, the gas motor will be activated and you will have zero chance of using regenerative braking until the car switches back to the electric motor.  What you need to do is to lightly touch the gas pedal, and then to gradually start to increase your speed.  Just remember that you are not in the middle of a race,  you are simply going to a close-by destination.  By delicately pushing the gas pedal, you will remain in the electric mode.  As soon as you have the chance to glide along without having to use the gas pedal, do so. Regenerative braking will kick in.

Regenerative Braking Feels Odd at First

Regenerative braking feels strange at first.  It is as if the hybrid is being held back by an invisible force.  Just keep in mind that this is normal and that this reversal of torque is going to generate free current for you to use.  I have found the torque reversal is slightly different from the feeling you get when you release the gas pedal in a normal car.  It causes you to slow down a tiny bit faster.

Releasing the gas pedal will initiate regenerative braking right away on most hybrids; however, if your hybrid has an ECO mode for the electric motor, use it when within a city.  I did not even realize that it helped to increase the regenerative braking sessions.  I thought the ECO meant that I shotting out less exhaust when the gas motor was being used.

ECO mode for Regenerative Braking Enhancement

The ECO mode is something that I use a lot now and I have noticed that my driving range has increased even more than before.  Not only does it increase the sensitivity for the sensors when the car should be using regenerative braking, but it decreases the power used by the electric motor by lowering the torque.  That is fine when driving around in a city or a small town, where you do not need to accelerate to 60 miles an hour in 5 seconds.

Using the ECO mode and other tactics will cause more regenerative braking.  But what happens to the brakes when the battery is full? This can happen if you are gung-ho about initiating regenerative braking constantly.  This is when the normal friction brakes will need to take over causing the wear and tear of the brake pads.  Another feature besides ECO is the B or braking mode.

At first, I thought that this meant that the car would be braking easier when using regenerative braking.  I was wrong, it opens air valves so that the axles will slow down even more so.  Nevertheless, it does not slip into another gear as some people believe.

When should you turn on the braking mode?

I would say not too worry about it in most instances.  Nevertheless, if you are descending a huge hill, it would be best to turn it on.  If you do not, when your battery pack becomes fully charged due to the quick and full use of regenerative braking on a huge decline, then your friction brakes will be overused and perhaps even start to burn out.  I am not saying that you are in danger of losing your brakes completely,  I am just saying that you will wear down your brake pads faster.

When do the regular brakes take over the braking function in a Hybrid?

Knowing when the regular brakes take over will help you to stay in the regenerative mode.  I find that my friction brakes only seem to engage when I am almost stopped. Also, if I need to stop quickly, hitting hard on the brakes will make the pedal seem as if it is stuck, this is because of the fact that the hydraulic brakes are taking over quickly.

It might take you some time to learn how to sense when the friction brakes are kicking in.  As I had mentioned, there will be a difference that you can feel in the stiffness of the brake pedal.

You can also watch the indicator on the dash that shows when the regenerative braking reading is maxed out.  At this point, the friction brakes are about to take over.  It would then be best to keep the same pressure on the brakes until you almost come to a complete stop to maintain a good level of current being produced.

Watching constantly the dashboard is not advisable, you need to keep your eyes on the road.  After a few weeks, you will be able to feel when the brake pedal is tightening up meaning that hydraulic brakes are about to take over.

Another reason for sensing when regenerative braking is going to over-ridden by the friction brakes is that it will give you a chance to save on your brake pads.  If you are using the friction brakes too often, there will be more wear on the brake pads.

In a hybrid, the wear on the brake pads is usually not the same for all four brake pads.  With a hybrid, the rear brake pads will wear down faster because the rear wheels are used to brake more often when slowly coming to a stop.

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