New Bosch iBooster for improved braking control, more complete capture of braking energy in hybrids and EVs
|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.