Comfort braking—a feature that might seem minor—is making its way into more and more cars, with companies putting serious effort into fine-tuning it.
Bosch, a key player in automotive technology, introduced comfort braking years ago. Naturally, as a supplier, Bosch approached the issue through its core expertise: braking systems. The BYD Han was one of the first models to adopt it, and now Xpeng Motors’ Mona 03 has followed suit. Today, it’s a widely accepted solution in electric vehicles.
However, not all automakers have followed the same path. Last year, Li Xiang, CEO of Li Auto, revealed on Weibo that the braking products from suppliers like Bosch deliver braking products as “black boxes,” with no transparency into the underlying code. So, Li Auto developed an alternative: using CDC shock absorbers to soften the jerks caused by braking and acceleration. However, some users found the solution lacking—it didn’t fully eliminate the excessive swaying that’s common in EVs.
Meanwhile, Huawei, known for its robust R&D, took a different approach. In its Aito and Luxeed models, Huawei initially used a similar suspension system to reduce sway. But with the Aito M9, Huawei decided to use the vehicle’s motor drive to counteract the inertia that causes discomfort during braking.
Why braking comfort matters
There are two main reasons electric car makers care about braking comfort. First, EVs weigh more than gasoline cars, leading to greater inertia when stopping. Second, regenerative braking—a feature that recycles energy back into the battery—intensifies the overall braking force, meaning the car stops more abruptly, releasing inertia more suddenly.
The result? EVs are more prone to swaying during braking, leading many passengers to experience motion sickness.
For new drivers, learning how to brake without jerking is essential. Experienced drivers often brake softly or in short bursts to smooth out the braking process. These techniques work well in EVs, but reducing vehicle weight would be a more permanent solution, though it’s a complex engineering task. For now, automakers generally focus on refining how braking force is applied.
Most cars still rely on disc brakes, where brake pads press against the disc to generate friction and slow the wheels. In those moments when the pads clamp and release, passengers often feel jolted forward, which is what makes braking uncomfortable. The key to smooth braking is avoiding too much force at once.
EVs, however, add an extra layer: regenerative braking. This process converts potential energy into kinetic energy, providing additional stopping power. But it also shortens the braking distance, worsening the nosedive effect.
To solve this issue, Bosch introduced its comfort braking system.
A Bosch engineer explained to 36Kr that the core of this system is calculating the minimum braking force required for a given situation and releasing any excess force applied by the driver, helping to avoid abrupt braking. This method helps prevent harsh braking forces at the system level.
The calculation is simple enough. The system assesses the vehicle’s speed, road incline, and factors like brake pad friction, tire grip, and braking force distribution to determine the minimum force needed. The real challenge lies in controlling how this braking force is applied.
The art of smooth braking
Sudden braking—or even abruptly lifting your foot off the pedal—can cause the vehicle to sway, all thanks to rapid speed changes. The essence of comfort braking lies in keeping the process smooth.
Experienced drivers often coast to a stop by gently easing off the gas pedal or applying the brakes in short, controlled bursts, reducing deceleration and ensuring a smoother stop. Engineers designing comfort braking systems aim to replicate this, smoothing out the process of applying and releasing braking force. But smooth doesn’t mean a straight line from point A to B—it’s about making the deceleration feel natural, as if an experienced driver were behind the wheel. Since every car has different hardware, each one requires a tailored braking curve.
Take the Nio ES6 as an example. With comfort braking engaged, the nosedive effect during braking is noticeably reduced. This improvement is not reliant on the driver’s skill; the system automatically ensures smoother braking, regardless of who’s behind the wheel.
Consumers, however, may wonder whether comfort braking increases stopping distances and poses safety concerns.
Bosch engineers told 36Kr that comfort braking is only activated under specific conditions. In emergencies, the system prioritizes the driver’s requested braking force, regardless of comfort settings. The system monitors the vehicle’s deceleration and disables comfort braking if the situation calls for an emergency stop. This technology is mature and has already been widely adopted.
When comfort braking is engaged, the system can extend the stopping distance by about 40 centimeters. In non-emergency situations, however, this additional distance does not impact safety.
All of these comfort braking functions rely on a brake-by-wire system, a relatively new chassis technology that has only been in production for a few years. Currently, only a small number of models—such as the BYD Han and Nio ES6—are equipped with this technology.
So, what about older EV models that don’t have this feature but could benefit from comfort braking? The solution involves applying force to counteract inertia during braking.
Is active suspension the solution?
One way to combat inertia is by using the motor drive.
In simple terms, even while braking, the car’s motor drive can be activated to counteract the vehicle’s forward momentum. However, brake suppliers must adhere to strict safety standards. The motor drive should never override the brake pedal or take control away from the driver.
At the launch of the Aito S9, Huawei figurehead Richard Yu explained that the company has invested significant effort in negotiating with suppliers to update braking features. Clearly, this technology is no mean feat to implement on a large scale.
Another option is to use the suspension system to absorb and filter the forces generated during braking.
Suspension systems balance two opposing goals—vehicle stability and passenger comfort. A stiffer suspension helps maintain stability during sharp turns and hard braking but offers little relief from road bumps. A softer suspension smooths out the ride but can lead to nosedive during braking or lift when accelerating.
An engineer explained to 36Kr that using suspension to improve braking comfort means carefully adjusting the suspension’s ability to reduce sway. For example, in the Luxeed S7—equipped with Huawei’s Turing chassis—the comfort braking system significantly reduces body pitch during both acceleration and braking.
The core of the system is the CDC shock absorbers, which adjust the suspension damping in milliseconds to stabilize the vehicle’s body during braking. Springs play a crucial role, too, by hardening at the moment of braking to resist nosedive and damping the rebound once the brakes are released. The key to making this work is the speed and precision of these adjustments.
Traditional mechanical shock absorbers only adjust a few times per second. However, continuous damping control (CDC) shock absorbers can adjust up to 100 times per second, giving cars equipped with them a significant advantage. But tuning suspension systems remains more of an art than a science, relying heavily on experience and rigorous testing.
Suspension layout, vehicle weight, and chassis design all influence the tuning outcome. Poor tuning can even make the problem worse. Only a few companies have both the technology and the expertise to implement CDC shock absorbers effectively. As brake-by-wire systems become more widespread, it’s likely that supplier-developed solutions will dominate the market due to their lower cost and simpler implementation.
Still, safety remains the number one priority. Comfort braking is an auxiliary function meant to improve the driving experience by reducing motion sickness, but it doesn’t replace the driver’s role in braking safely. The key to balancing safety and comfort lies in maintaining good driving habits.
KrASIA Connection features translated and adapted content that was originally published by 36Kr. This article was written by Xu Caiyu for 36Kr.