New Bosch iBooster for improved braking control, more complete capture of braking energy in hybrids and EVs
18 June 2013
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| The iBooster. Click to enlarge. |
Bosch has developed the iBooster, an electromechanical brake booster that provides situation-dependent support when the driver initiates braking. The iBooster makes hybrid and electric vehicles even more efficient, while enhancing safety through shorter braking distances, says Gerhard Steiger, president of the Bosch Chassis Systems Control division.
For hybrid and electric vehicles to achieve their intended range and fuel efficiency, they must recover as much electrical drive energy as possible when braking. Ideally, cars would be slowed down purely as a result of their electric motor converting their kinetic energy into electricity, avoiding the loss of valuable energy through braking. The Bosch iBooster recovers almost all the energy lost in typical braking operations by ensuring deceleration rates of up to 0.3 g are achieved using the electric motor alone. It thus covers all common braking maneuvers in everyday traffic.
If the brakes to be applied harder, the iBooster generates the additional braking pressure needed in the traditional way, using the brake master cylinder. The driver does not notice this interplay of motor and brakes, as pedal feel remains absolutely normal, according to Bosch.
Bosch has integrated a motor into the iBooster to control the degree of brake boosting via a two-stage gear unit for situation-dependent support on demand. This dispenses with the current costly, continuous process of generating a vacuum using either the internal combustion engine directly or a vacuum pump. In addition to saving fuel, it also allows more comprehensive use of fuel-saving functions that stop the engine for periods of time, such as start-stop or coasting.
The electromechanical concept offers further advantages. Should the predictive emergency braking system detect a dangerous situation, the iBooster can build up full braking pressure autonomously in 120 milliseconds or so—three times faster than previous systems. In emergency situations, therefore, the iBooster can brake the vehicle faster than a driver using a conventional braking system.
The iBooster can also take on the Adaptive Cruise Control’s (ACC’s) job of gently bringing the vehicle to a standstill, and do so comfortably and noiselessly. This is particularly compelling for quiet e-vehicles, since ambient sounds are much more noticeable in their interior.
The ability to define characteristic braking curves gives developers the freedom to determine pedal feel and adapt it to the customer's brand-specific wishes. If the vehicle also offers driving modes such as sport, comfort, or economy, the brakes can be made to react more softly or more aggressively as appropriate. Situation-dependent support is also possible, for instance during emergency braking.
With a freely programmable braking performance curve, identical Bosch iBoosters can be installed in different variants of a vehicle model and still offer tailored characteristics. Programming is quick and easy at the end of the production line, and it is easy to vary the installation to suit right-hand-drive or left-hand-drive models, according to Bosch.
The booster unit itself is purely electromechanical, without brake fluid, which means it can be rotated flexibly about the longitudinal axis. Consideration has also been given to the future of car driving: in combination with Bosch ESP, the system offers the level of braking-system redundancy that is needed for safety reasons in automated self-driving cars.
The iBooster complements a modular range of components from which Bosch can assemble a suitable braking system for many different vehicle configurations. Production of the new iBooster will start in 2013 for three series-produced models.
It would be nice to know what the current efficiencies are and what this device actually delivers.
Posted by: TM | 18 June 2013 at 09:17 AM
That shows Bosch is really commited to electrification. Integration two braking systems always an issue. Chevy Volt and Prius are regenerating when acceleration pedal off. Here no comprromising system - braking starts when braking pedal on. This could be real game changer.
Posted by: Darius | 18 June 2013 at 11:08 AM
@TM
Agree.
Posted by: ai_vin | 18 June 2013 at 05:19 PM
Actually the Toyota hybrids have been doing this for 10 years, so no big news here. Think Ford does it too but can't say for sure.
Posted by: Dave K. | 19 June 2013 at 05:17 AM
Is this better than the Toyota system?
Posted by: HarveyD | 19 June 2013 at 08:58 AM
Yes, the Prius does not execute its regenerative braking in this way but maybe the next generation will.
We can hope anyway...
"The ability to define characteristic braking curves gives developers the freedom to determine pedal feel and adapt it to the customer's brand-specific wishes. If the vehicle also offers driving modes such as sport, comfort, or economy, the brakes can be made to react more softly or more aggressively as appropriate. Situation-dependent support is also possible, for instance during emergency braking."
With the Prius you have basically two curves and the brake pads begin to move as soon as you apply the brakes. The more aggressive curve is initiated only when you put the drive lever into "B".
With this system it sounds like the brake pads themselves do not move unless there is an emergency where more than 0.3g of deceleration is needed. Most people never experience more than 0.2g in longitudinal acceleration even when driving aggressively in a sporty car.
What this means is that this system would save your brakes even more allowing for some down-sizing of the rotors further increasing fuel economy and reducing upfront and maintenance costs.
Posted by: Trevor Carlson | 21 June 2013 at 08:08 AM
This is interesting but... why to reinvent the wheel? If propulsion electrical system is powerful enough (at least peak power powerful enough) it is able to provide breaking deceleration as high as 1g (whatever tires allow). So, the iBoost is an intermediate (handicapped) solution before normal series hybrids take over industry. I would be delighted to work on supercaps + battery energy storage system capable of absorbing full breaking energy. In this case semiconductors must be rated for high power for short runs but system's cooling capability should be designed for average power only.
Posted by: CarCrazy | 26 June 2013 at 12:44 PM
To me it looks like brake-by-wire.
Unless there is a mechanical bypass in the Bosch iBooster device that activates hydraulic brakes whenever the brake pedal is pressed beyond certain preset position in pedal travel. The description above doesn't suggest mechanical activation of hydraulic brakes, caused by brake pedal move, regardless of electronic system of iBooster.
If hydraulic brakes are activated only electronically by iBooster device, it means that failure in iBooster results in brake failure, no redundant system is mentioned.
On the other hand the iBooster device greatly simplifies implementation of regen braking in hybrid vehicles. Not mentioned, but iBooster must be provided with software interface that sends messages to braking e-motor control electronics specifying the braking torque to be applied by e-motor. It doesn't need return info from motor controller, if e-motor didn't provide desired deceleration within expected time interval, iBooster activates hydraulic brakes. I guess iBooster software needs to be customized for the e-motor used for braking, i.e. it needs to know e-motor's max braking torque.
Reportedly seamless regen braking is one of the most difficult things to achieve in hybrid vehicles. Now there is Bosch iBooster to take care of it.
Posted by: Alex_C | 27 June 2013 at 06:34 PM