Mercedes Regenerative Braking - How It Works
On an electric or hybrid Mercedes, regenerative braking (Mercedes calls it recuperation) works by running the electric motor as a generator when you lift off the accelerator or press the brake. The wheels turn the motor, the motor slows the car, and the electricity it makes goes back into the high-voltage battery instead of being lost as heat at the brake discs. On most electric Mercedes models you choose how strongly it does this with the paddles behind the steering wheel.
Conventional friction brakes turn that energy into heat and waste it. Because the motor does a lot of the slowing, the pads and discs also wear more slowly, and the car becomes more efficient overall.
Energy can be stored chemically in a battery, electrically in a bank of capacitors, or mechanically in a spinning flywheel in battery-electric and hybrid electric cars. In a hydrogen fuel cell vehicle, the electricity from the motor is stored in a battery, just like in battery- and hybrid-electric cars.
TL;DR
- Cause of the slowing: the electric motor works as a generator and charges the high-voltage battery.
- It can recover up to 70% of the kinetic energy that would otherwise be lost when braking.
- It kicks in when you press the brake and when you lift off the accelerator.
- Mercedes offers five recuperation settings on the paddles: D--, D-, D, D+ and D Auto.
- D-- gives the strongest recovery and turns on the brake lights; D+ coasts with no recovery.
- Friction brakes are still fitted and still need regular checks.
If your concern is brake dust on the wheels rather than how regen works, read how to remove Mercedes brake dust.
The Table of Content
- Regenerative Braking: What Is It?
- How Does Regenerative Braking Work?
- What Does Mercedes' Recuperation Braking Do?
- Which Mercedes Models are Equipped with Recuperation Braking?
- How Much Charge Does Regenerative Braking Add?
- What are the Advantages of Regenerative Braking?
- What are the Disadvantages of Regenerative Braking?
- What Does Regenerative Braking Feel Like?
- How Do PlugIn Hybrid and Electric Mercedes Automobiles Use Regenerative Braking?
- How Is Regenerative Braking Efficiency Calculated?
- The Conclusion
1. Regenerative Braking: What Is It?
Most hybrid and fully electric cars use regenerative braking. It turns the kinetic energy from braking into electrical power to charge the car's high-voltage battery, and it helps the conventional brakes slow the vehicle down.
Image source: https://www.jdpower.com/cars/shopping-guides/what-is-regenerative-braking
In a traditional braking system, friction between the brake pads and rotors slows the car down. When you brake, almost all of the kinetic energy pushing the car forward is turned into heat and lost.
Regenerative braking recovers up to 70% of that kinetic energy. How much you get back depends on your car and your driving style.
2. How Does Regenerative Braking Work?
To understand regenerative braking, start with conventional brakes. When you press the brake pedal, the brake discs and brake pads come into contact with each other. The friction turns the car's kinetic energy into heat, which is released into the air.
With regenerative braking, that energy is recovered and turned into electricity instead. When you accelerate or cruise, the motor drives the wheels; when you slow down, the wheels drive the motor.
This two-way energy flow lets the motor act as a generator: it resists the rotation of the wheels and produces power to recharge the battery.
Regeneration happens in two situations:
- When the driver presses the brake.
- When the driver lifts off the accelerator and the car coasts.
In both cases the system makes power to top up the battery. You can see it on the car's charge gauge as energy flowing from the wheels to the battery.
The electrical output is proportional to the braking force: the harder the system brakes, the higher the current. How much energy it captures depends on the vehicle's speed and how long the brakes are applied.
When you brake, the car automatically splits the braking force between the traditional brakes and energy recovery. It slows the car and recharges the battery at the same time, which improves economy and electric range.
Image source: https://www.howtogeek.com/788914/what-is-regenerative-braking/
The U.S. Department of Energy's fueleconomy.gov describes the same principle for hybrid vehicles: regenerative braking uses the forward motion of the wheels to turn the motor, which generates electricity and helps slow the vehicle.
3. What Does Mercedes' Recuperation Braking Do?
Mercedes cars use recuperation to recover energy while decelerating, which helps you manage your range. The shift paddles offer five recuperation modes. The stronger the recuperation, the more energy the car recovers and the faster it slows down:
- D-- Choose this to get the most range (Mercedes describes it for the Vito Tourer). It recovers the most energy and decelerates the fastest. Because the deceleration is strong, the brake lights turn on automatically.
- D- When you lift off, the car slows down and recovers energy a little more gently than in D--. In most cases this setting turns on the brake lights.
- D Useful for holding a fairly steady speed in busier traffic. The car returns to D each time you restart it. It feels like a steady slowdown, similar to dropping a diesel car into a lower gear. Some energy is recovered, but less than in D-. This setting usually does not turn on the brake lights.
- D+ This is a sailing mode: the car slows down naturally, like a diesel car coasting to a halt, and the battery recovers no energy. It lets you "surf" without drag from the electric motor on long downhill stretches of main roads.
- D Auto Engaged with a long pull on either paddle. It uses a radar sensor and navigation data to adapt the recuperation level to the traffic for you.
| Mode | Recuperation | Brake lights | When to use it |
|---|---|---|---|
| D-- | Strongest, fastest deceleration | Turn on automatically | Maximum range |
| D- | Strong, a little gentler than D-- | Usually on | Strong recovery with softer slowing |
| D | Moderate (default after restart) | Usually off | Steady speed in traffic |
| D+ | None (sailing) | Off | Long downhill or open road coasting |
| D Auto | Adapts automatically | Depends on deceleration | Let ECO Assist decide |
4. Which Mercedes Models are Equipped with Recuperation Braking?
An all-electric drive can reverse the direction of energy conversion and so recover energy.
During acceleration the electric motor takes electrical energy and produces mechanical energy. During deceleration the vehicle's kinetic energy drives the motor, which produces electrical energy.
That energy is fed back into the high-voltage battery and used again to drive the car. Five recovery modes are available on the Mercedes-Benz B Class, EQE, EQC, EQS and EQA.
The shift paddles on the steering wheel adjust how much braking energy is fed back, from "D+" (gliding) to "D--" (strong recuperation). In D Auto, ECO Assist controls the strength of recovery according to the driving conditions. On the current EQS sedan, Mercedes-Benz USA lists "Intelligent Energy Recovery with paddles" with normal, increased and no recuperation, plus a D Auto setting that activates ECO Assist.
Image source: forbes.com (Forbes Wheels, "Regenerative braking")
5. How Much Charge Does Regenerative Braking Add?
Regenerative braking can recover up to 70% of the kinetic energy that would otherwise be lost as heat when braking. The amount of charge you actually get back depends on your car, your speed, how long you brake and your driving style; the faster you are going, the more energy there is to recover.
Electric drive is efficient to begin with: according to fueleconomy.gov, EVs convert over 77% of the electrical energy from the grid to power at the wheels, while conventional gasoline vehicles convert only about 12% to 30% of the energy stored in gasoline.
6. What are the Advantages of Regenerative Braking?
Capturing and reusing more braking energy makes your car more efficient and wears your brakes less. These are the main benefits:
6.1 Rotors and Pads for Brakes Could Last Longer
EVs and hybrids still have standard hydraulic brakes. Because regenerative braking does much of the work of slowing the car, the pads and rotors are used much less.
As a result they usually need fewer repairs, which can save you money on maintenance.
You should still have the brakes checked regularly, and the manufacturer's maintenance schedule may include regular inspections.
6.2 EVs Possibilities for Extended Range
Recapturing braking energy and sending it straight back to the battery pack increases your EV's range. Estimates suggest regenerative braking can add hundreds of miles of range per year, so you spend less on charging and more time driving.
Image source: treehugger.com ("How does regenerative braking work")
Every mile counts where chargers are still scarce. Using the grid less also cuts emissions from power stations that burn coal and gas.
6.3 Better Hybrid Fuel Efficiency
Hybrids still have a combustion engine, but they are built to make the most of their electric powertrain. Regenerative braking helps keep the battery charged so the engine runs less often, which lowers fuel costs.
7. What are the Disadvantages of Regenerative Braking?
Regenerative braking has more advantages than disadvantages, but no technology is perfect. Here are the situations where it falls short:
7.1 At Lower Speeds, It Might Be Less Effective
At low speed the car has less kinetic energy and needs less braking, so the system sends less energy to the battery. Some automakers believe coasting can be better than regenerative braking in some situations.
7.2 The Brake Pedal Could Feel Peculiar
The brake pedals on hybrid and electric vehicles work, but they can feel different.
You may notice a brief lack of response or a pedal that doesn't compress as smoothly as you'd like, and you may need to modulate the pedal differently in different situations.
This is less of a problem than it used to be. On newer hybrid and electric models, the brake pedal is more responsive and feels like a standard brake.
7.3 Less Possible Stopping Power
Regenerative braking works well for most braking, which is a gradual slowdown. It may not deliver the same stopping power as conventional brakes, so drivers of hybrid and electric vehicles may need to press harder to get the same effect.
Image source: https://brakeexperts.com/why-is-regenerative-braking-limited/
Newer regenerative braking systems have improved here too. In recent models you may not notice any change in stopping power.
8. What Does Regenerative Braking Feel Like?
Every car with regenerative braking, from an electric Mercedes to rivals like the Volkswagen ID.4, behaves a little differently, and in most of them you can set it to your liking.
Set it to the highest level to recover as much energy as possible, or turn it off if you don't like how the car brakes. The brake lights usually come on if the car slows down sharply, even when you are not pressing the brake pedal.
Some adaptive cruise control systems also use brake regeneration: sensors track the car in front and regen is applied to match its speed.
In many EVs, lifting off the accelerator feels like your foot is still on the brake. You speed up and slow down by adjusting your right foot instead of switching between the brake and accelerator. This is called one-pedal driving.
9. How Do PlugIn Hybrid and Electric Mercedes Automobiles Use Regenerative Braking?
A plug-in hybrid electric vehicle (PHEV) has an internal combustion engine (ICE) that runs on fuel such as gasoline, and an electric motor powered by batteries.
PHEV batteries can be charged by the ICE, a power outlet, a charger, or regenerative braking. The car normally uses ICE power until the battery is nearly empty, then switches back to electric power.
Regenerative braking uses the car's forward motion when you lift off the accelerator to recharge the onboard batteries.
It converts momentum back into electrical energy for later use. Like an old bicycle with wheel-driven dynamo lights, it stops producing power when the car stops moving.
Image source: import-car.com ("Regenerative braking service")
10. How Is Regenerative Braking Efficiency Calculated?
One method for working out how much regenerative braking an environmentally friendly car should use follows these steps:
- Determine whether regenerative braking is active.
- Determine whether a high-voltage component, such as the battery or drive motor, limits charging while regenerative braking is in use.
- Calculate the base speed (base rpm) of the drive motor during regenerative braking from the charging limit, and divide the steady torque and steady power areas at that base speed.
- Using those areas, decide whether the drive motor is in steady power mode, steady torque mode or a conversion mode, and calculate the amount of regenerative braking from the result.
11. The Conclusion
Hybrid and electric cars rely on battery technology, aerodynamics and other engineering to be efficient, and regenerative braking is one of the key pieces. It reuses energy that would otherwise be lost when stopping to help recharge the battery.
Because it reduces wear and wasted energy, regenerative braking also increases electric range and brake life.