Sensotronic Brake Actuation: Notes
The brake system of E72 serves not only to decelerate the vehicle in a safe and stable manner. It also enables the braking energy of the vehicle to be not converted into heat, but instead recovered and converted into electrical energy using the electric machines in the active gearbox. To attain maximum fuel economy in conjunction with the full hybrid drive of the E72, the brake system must be able to recover as much brake energy as possible. At the same time, the customer has the right to expect the typical BMW brake pedal feeling, exact controllability of the brake force and, of course, outstanding deceleration values in all speed ranges and driving situations. Of course, the hybrid brake system of the E72 meets all of these requirements, thus proving the technological expertise of the BMW Group in this area.
To meet these requirements, a brake system has been developed in which there is not a permanent mechanical connection between the brake pedal and the rest of the brake system (brake servo). Instead, it is a brake-by-wire system, which detects the driver's braking request electronically. Then, the braking request is split into an electrical portion and a hydraulic portion. The electrical portion is converted to electrical energy by the electric machines of the active gearbox and stored in the high voltage battery. The hydraulic portion generates deceleration via the conventional service brake. The braking request is split according to its strength, the driving situation and the state of the hybrid components. In this way, the hybrid brake system can implement decelerations of up to 3 m/s2 in pure electric mode. However, a much more important parameter is the percentage of brake energy that can be recovered, across all driving situations. Here, the complex brake system of the E72 attains a very high value of between 80% and 90% - conversely, this means that only 10% to 20% of the entire brake energy is converted into useless heat via the service brake.
| Index | Explanation |
|---|---|
| 1 | Brake pedal |
| 2 | Active brake servo |
| 3 | Brake fluid expansion tank |
| 4 | Vacuum line |
| 5 | Mechanical vacuum pump |
| 6 | Electrical vacuum pump |
| 7 | Dynamic stability control |
| 8 | Hybrid brake actuation changeover (Sensotronic Brake Actuation SBA) |
| Index | Explanation |
|---|---|
| 1 | Hybrid brake actuation changeover (Sensotronic Brake Actuation SBA) |
| 2 | Sensor for brake vacuum |
| 3 | Solenoid valve for activating the active brake servo |
| 4 | Sensor for diaphragm travel |
| 5 | Brake pressure sensor, pressure chamber |
| 6 | Brake pressure sensor, floating circuit |
| 7 | Pressure sensor of the shut-off unit |
| 8 | Valve in the shut-off unit |
| 9 | Sensor for brake pedal angle |
| 10 | Lines for controlling and monitoring the electrical vacuum pump |
| 11 | Dynamic Stability Control (DSC) |
| 12 | Electrical vacuum pump |
| 13 | Hybrid Interface Module HIM |
| 14 | Junction box electronics |
| 15 | Electromechanical relay for activating the electrical vacuum pump |
| 16 | Semiconductor relay for activating the electrical vacuum pump |
| 17 | Hybrid fuse block |